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  INTERNET-DRAFT                   Geoffrey Clemm, Rational Software
  draft-ietf-deltav-versioning-15  Jim Amsden, IBM
                                   Chris Kaler, Microsoft
                                   Jim Whitehead, U.C. Santa Cruz
  
  Expires October 17, 2001         April 17, 2001
  
                       Versioning Extensions to WebDAV
  
  Status of this Memo
  This document is an Internet-Draft and is in full conformance with all
  provisions of RFC 2026, Section 10.
  
  Internet-Drafts are working documents of the Internet Engineering Task
  Force (IETF), its areas, and its working groups.  Note that other groups
  may also distribute working documents as Internet-Drafts.
  
  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents at any
  time.  It is inappropriate to use Internet-Drafts as reference material
  or to cite them other than as "work in progress."
  
  The list of current Internet-Drafts can be accessed at
  http://www.ietf.org/ietf/1id-abstracts.txt
  
  The list of Internet-Draft Shadow Directories can be accessed at
  http://www.ietf.org/shadow.html.
  
  
  Abstract
  This document specifies a set of methods, headers, and resource types
  that define the WebDAV Versioning extensions to the HTTP/1.1 protocol.
  WebDAV Versioning will minimize the complexity of clients that are
  capable of interoperating with a variety of versioning repository
  managers, to facilitate widespread deployment of applications capable of
  utilizing the WebDAV Versioning services.  WebDAV Versioning includes:
       - Automatic versioning for versioning-unaware clients,
       - Version history management,
       - Workspace management,
       - Baseline management,
       - Activity management, and
       - URL namespace versioning.
  
  
  
  
  
  
  
  
  
  
  
  
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  Table of Contents
  
  1 INTRODUCTION...........................................7
  1.1 Relationship to WebDAV...............................7
  1.2 Notational Conventions...............................8
  1.3 Terms................................................8
  1.4 Property Values.....................................11
   1.4.1 Initial Property Value...........................11
   1.4.2 Protected Property Value.........................11
   1.4.3 Computed Property Value..........................12
   1.4.4 Boolean Property Value...........................12
   1.4.5 DAV:href Property Value..........................12
  1.5 DAV Namespace XML Elements in Request and Response
      Bodies..............................................12
  1.6 Response Bodies for 403 and 409 Status Responses....12
   1.6.1 Example - CHECKOUT request with
         DAV:must-not-be-checked-out response.............13
  1.7 Clarification of COPY Semantics with Overwrite:T....13
  1.8 Versioning Methods and Write Locks..................14
  
  2 BASIC VERSIONING FEATURES.............................14
  2.1 Basic Versioning Packages...........................14
  2.2 Basic Versioning Semantics..........................15
   2.2.1 Creating a Version-Controlled Resource...........15
   2.2.2 Modifying a Version-Controlled Resource..........17
   2.2.3 Reporting........................................19
  
  3 VERSION-CONTROL FEATURE...............................19
  3.1 Additional Resource Properties......................19
   3.1.1 DAV:comment......................................19
   3.1.2 DAV:creator-displayname..........................19
   3.1.3 DAV:supported-method-set (protected).............20
   3.1.4 DAV:supported-live-property-set (protected)......20
   3.1.5 DAV:supported-report-set (protected).............20
  3.2 Version-Controlled Resource Properties..............20
   3.2.1 DAV:checked-in (protected).......................20
   3.2.2 DAV:auto-checkout................................21
   3.2.3 DAV:auto-checkin.................................21
  3.3 Checked-Out Resource Properties.....................21
   3.3.1 DAV:checked-out (protected)......................22
   3.3.2 DAV:predecessor-set..............................22
   3.3.3 DAV:precursor-set................................22
  3.4 Version Properties..................................22
   3.4.1 DAV:predecessor-set (protected)..................22
   3.4.2 DAV:successor-set (computed).....................22
   3.4.3 DAV:checkout-set (computed)......................22
   3.4.4 DAV:version-name (protected).....................23
   3.4.5 DAV:precursor-set (protected)....................23
  3.5 VERSION-CONTROL Method..............................23
   3.5.1 Example - VERSION-CONTROL........................24
  3.6 REPORT Method.......................................24
  3.7 DAV:version-tree REPORT.............................25
   3.7.1 Example - DAV:version-tree REPORT................26
  3.8 Additional OPTIONS Semantics........................27
  
  
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  3.9 Additional PUT Semantics............................27
  3.10 Additional PROPFIND Semantics......................28
  3.11 Additional PROPPATCH Semantics.....................28
  3.12 Additional DELETE Semantics........................29
  3.13 Additional COPY Semantics..........................29
  3.14 Additional MOVE Semantics..........................30
  3.15 Additional UNLOCK Semantics........................30
  
  4 CHECKOUT FEATURE......................................31
  4.1 Additional Version Properties.......................31
   4.1.1 DAV:checkout-fork................................31
   4.1.2 DAV:checkin-fork.................................32
  4.2 CHECKOUT Method.....................................32
   4.2.1 Example - CHECKOUT of a version-controlled
         resource.........................................33
  4.3 CHECKIN Method......................................34
   4.3.1 Example - CHECKIN................................35
  4.4 UNCHECKOUT Method...................................35
   4.4.1 Example - UNCHECKOUT.............................36
  4.5 Additional OPTIONS Semantics........................36
  
  5 VERSION-HISTORY FEATURE...............................36
  5.1 Version History Properties..........................37
   5.1.1 DAV:version-set (protected)......................37
   5.1.2 DAV:root-version (computed)......................37
  5.2 Additional Version-Controlled Resource Properties...37
   5.2.1 DAV:version-history (computed)...................37
  5.3 Additional Version Properties.......................37
   5.3.1 DAV:version-history (computed)...................37
  5.4 DAV:locate-history REPORT...........................38
   5.4.1 Example - DAV:locate-history REPORT..............38
  5.5 Additional OPTIONS Semantics........................39
  5.6 Additional DELETE Semantics.........................40
  5.7 Additional COPY Semantics...........................40
  5.8 Additional MOVE Semantics...........................40
  5.9 Additional VERSION-CONTROL Semantics................41
  5.10 Additional CHECKIN Semantics.......................41
  
  6 WORKSPACE FEATURE.....................................41
  6.1 Workspace Properties................................42
   6.1.1 DAV:workspace-checkout-set (computed)............42
  6.2 Additional Resource Properties......................42
   6.2.1 DAV:workspace (protected)........................42
  6.3 MKWORKSPACE Method..................................42
   6.3.1 Example - MKWORKSPACE............................43
  6.4 Additional OPTIONS Semantics........................43
  6.5 Additional DELETE Semantics.........................44
  6.6 Additional MOVE Semantics...........................44
  6.7 Additional VERSION-CONTROL Semantics................45
   6.7.1 Example - VERSION-CONTROL (using an existing
         version history).................................45
  
  7 UPDATE FEATURE........................................46
  7.1 UPDATE Method.......................................46
   7.1.1 Example - UPDATE.................................47
  7.2 Additional OPTIONS Semantics........................47
  
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  8 LABEL FEATURE.........................................47
  8.1 Additional Version Properties.......................48
   8.1.1 DAV:label-name-set (protected)...................48
  8.2 LABEL Method........................................48
   8.2.1 Example - Setting a label........................49
  8.3 Label Header........................................50
  8.4 Additional OPTIONS Semantics........................50
  8.5 Additional GET Semantics............................50
  8.6 Additional PROPFIND Semantics.......................51
  8.7 Additional COPY Semantics...........................51
  8.8 Additional CHECKOUT Semantics.......................52
  8.9 Additional UPDATE Semantics.........................52
  
  9 WORKING-RESOURCE FEATURE..............................53
  9.1 Working Resource Properties.........................53
  9.2 Additional OPTIONS Semantics........................54
  9.3 Additional COPY Semantics...........................54
  9.4 Additional MOVE Semantics...........................54
  9.5 Additional CHECKOUT Semantics.......................54
   9.5.1 Example - CHECKOUT of a version..................55
  9.6 Additional CHECKIN Semantics........................55
   9.6.1 Example - CHECKIN of a working resource..........55
  
  10  ADVANCED VERSIONING FEATURES........................56
  10.1 Rationale..........................................56
  10.2 Advanced Versioning Terms..........................56
  10.3 Advanced Versioning Packages.......................57
  
  11  MERGE FEATURE.......................................58
  11.1 Additional Checked-Out Resource Properties.........58
   11.1.1 DAV:merge-set...................................59
   11.1.2 DAV:auto-merge-set..............................59
  11.2 MERGE Method.......................................59
   11.2.1 Example - MERGE.................................62
  11.3 DAV:merge-preview REPORT...........................63
   11.3.1 Example - DAV:merge-preview REPORT..............63
  11.4 Additional OPTIONS Semantics.......................64
  11.5 Additional DELETE Semantics........................65
  11.6 Additional CHECKIN Semantics.......................65
  
  12  BASELINE FEATURE....................................65
  12.1 Version-Controlled Configuration Properties........66
   12.1.1 DAV:baseline-controlled-collection (protected)..66
  12.2 Checked-Out Configuration Properties...............66
   12.2.1 DAV:subbaseline-set.............................66
  12.3 Baseline Properties................................66
   12.3.1 DAV:baseline-collection (protected).............67
   12.3.2 DAV:subbaseline-set (protected).................67
  12.4 Additional Resource Properties.....................67
   12.4.1 DAV:version-controlled-configuration (computed).67
  12.5 Additional Workspace Properties....................67
   12.5.1 DAV:baseline-controlled-collection-set
          (computed)......................................67
  12.6 BASELINE-CONTROL Method............................68
   12.6.1 Example - BASELINE-CONTROL......................69
  
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  12.7 DAV:compare-baseline REPORT........................70
   12.7.1 Example - DAV:compare-baseline REPORT...........70
  12.8 Additional OPTIONS Semantics.......................71
  12.9 Additional MKCOL Semantics.........................71
  12.10 Additional COPY Semantics.........................72
  12.11 Additional CHECKOUT Semantics.....................72
  12.12 Additional CHECKIN Semantics......................72
  12.13 Additional UPDATE Semantics.......................73
  12.14 Additional MERGE Semantics........................74
  
  13  ACTIVITY FEATURE....................................74
  13.1 Activity Properties................................76
   13.1.1 DAV:activity-version-set (computed).............76
   13.1.2 DAV:activity-checkout-set (computed)............76
   13.1.3 DAV:subactivity-set.............................76
   13.1.4 DAV:current-workspace-set (computed)............76
  13.2 Additional Version Properties......................77
   13.2.1 DAV:activity-set................................77
  13.3 Additional Checked-Out Resource Properties.........77
   13.3.1 DAV:unreserved..................................77
   13.3.2 DAV:activity-set................................77
  13.4 Additional Workspace Properties....................78
   13.4.1 DAV:current-activity-set........................78
  13.5 MKACTIVITY Method..................................78
   13.5.1 Example - MKACTIVITY............................78
  13.6 DAV:latest-activity-version REPORT.................79
  13.7 Additional OPTIONS Semantics.......................79
  13.8 Additional DELETE Semantics........................80
  13.9 Additional MOVE Semantics..........................80
  13.10 Additional CHECKOUT Semantics.....................81
   13.10.1 Example - CHECKOUT with an activity............81
  13.11 Additional CHECKIN Semantics......................82
  13.12 Additional MERGE Semantics........................82
  
  14  VERSION-CONTROLLED-COLLECTION FEATURE...............83
  14.1 Version-Controlled Collection Properties...........85
   14.1.1 DAV:eclipsed-set (computed).....................85
  14.2 Collection Version Properties......................86
   14.2.1 DAV:version-controlled-binding-set (protected)..86
  14.3 Working Collection Properties......................86
   14.3.1 DAV:version-controlled-binding-set..............86
  14.4 Additional OPTIONS Semantics.......................86
  14.5 Additional DELETE Semantics........................87
  14.6 Additional MKCOL Semantics.........................87
  14.7 Additional COPY Semantics..........................87
  14.8 Additional MOVE Semantics..........................87
  14.9 Additional VERSION-CONTROL Semantics...............88
  14.10 Additional CHECKOUT Semantics.....................88
  14.11 Additional CHECKIN Semantics......................88
  14.12 Additional UPDATE and MERGE Semantics.............88
  
  15  OPTIONAL REPORTS....................................89
  15.1 DAV:expand-property REPORT.........................89
   15.1.1 Example - DAV:expand-property...................90
  
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  16  INTERNATIONALIZATION CONSIDERATIONS.................91
  
  17  SECURITY CONSIDERATIONS.............................92
  17.1 Auditing and Traceability..........................92
  17.2 Increased Need for Access Control..................93
  17.3 Security Through Obscurity.........................93
  17.4 Denial of Service..................................93
  
  18  IANA CONSIDERATIONS.................................93
  
  19  INTELLECTUAL PROPERTY...............................94
  
  20  ACKNOWLEDGEMENTS....................................94
  
  21  REFERENCES..........................................94
  
  22  AUTHORS' ADDRESSES..................................96
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  1  INTRODUCTION
  
       This document specifies a set of methods, headers, and properties
       that define the WebDAV versioning extensions to the HTTP/1.1
       protocol.  Versioning is concerned with tracking and accessing the
       history of important states of a web resource, such as a standalone
       web page.  The benefits of versioning in the context of the
       worldwide web include:
  
       - A resource has an explicit history and a persistent identity
       across the various states it has had during the course of that
       history.  It allows browsing through past and alternative versions
       of a resource.  Frequently the modification and authorship history
       of a resource is critical information in itself.
  
       - Resource states (versions) are given stable names that can
       support externally stored links for annotation and link server
       support.  Both annotation and link servers frequently need to store
       stable references to portions of resources that are not under their
       direct control.  By providing stable states of resources, version
       control systems allow not only stable pointers into those
       resources, but also well defined methods to determine the
       relationships of those states of a resource.
  
       WebDAV Versioning defines both basic and advanced versioning
       functionality.
  
       Basic versioning allows authors to:
       - Put a resource under version control
       - Determine whether a resource is under version control
       - Determine whether a resource update will automatically be
       captured as a new version.
       - Create and access distinct versions of a resource
  
       Advanced versioning provides additional functionality for parallel
       development and configuration management of sets of web resources.
  
       This document will first define the properties and method semantics
       for the basic versioning features, and then define the additional
       properties and method semantics for the advanced versioning
       features.  An implementer that is only interested in basic
       versioning should skip the advanced versioning sections (Section 10
       to Section 15).
  
  
  1.1 Relationship to WebDAV
  
       To maximize interoperability and the use of existing protocol
       functionality, versioning support is designed as extensions to the
       WebDAV protocol [RFC2518], which itself is an extension to the HTTP
       protocol [RFC2616].  All method marshalling and postconditions
       defined by RFC 2518 and RFC 2616 continue to hold, to ensure that
       versioning unaware clients can interoperate successfully with
  
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       versioning servers.  Although the versioning extensions are
       designed to be orthogonal to most aspects of the WebDAV and HTTP
       protocols, a clarification to RFC 2518 is required for effective
       interoperable versioning.  This clarification is described in
       Section 1.7.
  
  
  1.2 Notational Conventions
  
       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
       this document are to be interpreted as described in RFC 2119.
  
       The term "protected" is placed in parentheses following the
       definition of a protected property (see Section 1.4.2).
  
       The term "computed" is placed in parentheses following the
       definition of a computed property (see Section 1.4.3).
  
       When an XML element type in the "DAV:" namespace is referenced in
       this document outside of the context of an XML fragment, the string
       "DAV:" will be prefixed to the element type.
  
       When a precondition or postcondition of a method is defined in this
       document, the definition can be prefixed by a parenthesized XML
       element type.  If a precondition is violated by a request or a
       postcondition cannot be satisfied, the XML element of the violated
       precondition or unsatisfied postcondition will be returned in the
       response body (see Section 1.5).
  
  
  1.3 Terms
  
       This document uses the terms defined in RFC 2616, in RFC 2518, and
       in this section.  Section 2.2 defines the semantic versioning model
       underlying this terminology.
  
     Version Control, Checked-In, Checked-Out
  
       "Version control" is a set of constraints on how a resource can be
       updated.  A resource under version control is either in a "checked-
       in" or "checked-out" state, and the version control constraints
       apply only while the resource is in the checked-in state.
  
     Versionable Resource
  
       A "versionable resource" is a resource that can be put under
       version control.
  
     Version-Controlled Resource
  
       When a versionable resource is put under version control, it
       becomes a "version-controlled resource".  A version-controlled
  
  
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       resource can be "checked out" to allow modification of its content
       or dead properties by standard HTTP and WebDAV methods.
  
     Checked-Out Resource
  
       A "checked-out resource" is a resource under version control that
       is in the checked-out state.
  
     Version Resource
  
       A "version resource", or simply "version", is a resource that
       contains a copy of a particular state (content and dead properties)
       of a version-controlled resource.  A version is created by
       "checking in" a checked-out resource.  The server allocates a
       distinct new URL for each new version, and this URL will never be
       used to identify any resource other than that version.  The content
       and dead properties of a version never change.
  
     Version History Resource
  
       A "version history resource", or simply "version history", is a
       resource that contains all the versions of a particular version-
       controlled resource.
  
     Version Name
  
       A "version name" is a string chosen by the server to distinguish
       one version of a version history from the other versions of that
       version history.  Versions from different version histories may
       have the same version name.
  
     Predecessor, Successor, Ancestor, Descendant
  
       When a version-controlled resource is checked out and then
       subsequently checked in, the version that was checked out becomes a
       "predecessor" of the version created by the checkin.  A client can
       specify multiple predecessors for a new version if the new version
       is logically a merge of those predecessors.  When a version is
       connected to another version by traversing one or more predecessor
       relations, it is called an "ancestor" of that version.  The inverse
       of the predecessor and ancestor relations are the "successor" and
       "descendant" relations.  Therefore, if X is a predecessor of Y,
       then Y is a successor of X, and if X is an ancestor of Y, then Y is
       a descendant of X.
  
     Precursor
  
       When a version resource is copied, that version is the "precursor"
       of the new resource created at the destination of the copy.  Unlike
       the predecessor relation, which only tracks the evolution of the
       versions in a single version history, the precursor relation tracks
       the evolution of versions from one version history to another.
  
  
  
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     Root Version Resource
  
       The "root version resource", or simply "root version", is the
       version in a version history that is an ancestor of every other
       version in that version history.
  
     Workspace Resource
  
       A "workspace resource", or simply "workspace", is a collection that
       contains at most one version-controlled resource for a given
       version history (see Section 6).
  
     Working Resource
  
       A "working resource" is a checked-out resource created by the
       server at a server-defined URL when a version (instead of a
       version-controlled resource) is checked out.  Unlike a checked-out
       version-controlled resource, a working resource is a deleted when
       it is checked in.
  
     Fork, Merge
  
       When a second successor is added to a version, this creates a
       "fork" in the version history.  When a version is created with
       multiple predecessors, this creates a "merge" in the version
       history.  A server may restrict the version history to be linear
       (with no forks or merges), but an interoperable versioning client
       should be prepared to deal with both forks and merges in the
       version history.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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       The following diagram illustrates several of the previous
       definitions.  Each box represents a version and each line between
       two boxes represents a predecessor/successor relationship.  For
       example, it shows V3 is a predecessor of V5, V7 is a successor of
       V5, V1 is an ancestor of V4, and V7 is a descendant of V4.  It also
       shows that there is a fork at version V2 and a merge at version V7.
  
                       History of foo.html
  
                               +---+
         Root Version -------> |   | V1
                               +---+           ^
                                 |             |
                                 |             |
                               +---+           |
         Version Name ----> V2 |   |           | Ancestor
                               +---+           |
                               /    \          |
                              /      \         |
                         +---+       +---+
                         |   | V3    |   | V4
                      ^  +---+       +---+
                      |    |           |       |
         Predecessor  |    |           |       |
                         +---+       +---+     |
                         |   | V5    |   | V6  | Descendant
                         +---+       +---+     |
         Successor    |       \      /         |
                      |        \    /          |
                      v        +---+           v
                               |   | V7
                               +---+
  
     Label
  
       A "label" is a name that can be used to select a version from a
       version history.  A label can be assigned by either a client or the
       server.  The same label can be used in different version histories.
  
  
  1.4 Property Values
  
  
  1.4.1Initial Property Value
  
       Unless an initial value of a property of a given type is defined by
       this document, the initial value of a property of that type is
       implementation dependent.
  
  
  1.4.2Protected Property Value
  
       When a property of a specific kind of resource is "protected", the
       property value cannot be updated on that kind of resource except by
  
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       a method explicitly defined as updating that specific property.  In
       particular, a protected property cannot be updated with a PROPPATCH
       request.  Note that a given property can be protected on one kind
       of resource, but not protected on another kind of resource.
  
  
  1.4.3Computed Property Value
  
       When a property is "computed", its value is defined in terms of a
       computation based on the content and other properties of that
       resource, or even of some other resource.  When the semantics of a
       method is defined in this document, the effect of that method on
       non-computed properties will be specified; the effect of that
       method on computed properties will not be specified, but can be
       inferred from the computation defined for those properties.  A
       computed property is always a protected property.
  
  
  1.4.4Boolean Property Value
  
       Some properties take a Boolean value of either "false" or "true".
  
  
  1.4.5DAV:href Property Value
  
       The DAV:href XML element is defined in RFC 2518, Section 12.3.
  
  
  1.5 DAV Namespace XML Elements in Request and Response Bodies
  
       Although WebDAV request and response bodies can be extended by
       arbitrary XML elements, which can be ignored by the message
       recipient, an XML element in the DAV namespace MUST NOT be used in
       the request or response body of a versioning method unless that XML
       element is explicitly defined in an IETF RFC.
  
  
  1.6 Response Bodies for 403 and 409 Status Responses
  
       A 403 (Forbidden) status indicates that an error has occurred that
       the client cannot resolve, and therefore the request should not be
       resubmitted.  A 409 (Conflict) status indicates that an error has
       occurred that the client can resolve, after which the request could
       be resubmitted.  According to RFC 2616, Section 10.4: "The 4xx
       class of status code is intended for cases in which the client
       seems to have erred.  Except when responding to a HEAD request, the
       server SHOULD include an entity containing an explanation of the
       error situation, and whether it is a temporary or permanent
       condition."
  
       In order to allow better client handling of 403 and 409 responses,
       a distinct XML element type can be associated with each method
       precondition and postcondition of a request.  When a particular
       precondition is violated or a particular postcondition cannot be
  
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       satisfied, the appropriate XML element MUST be returned as the
       child of a top-level DAV:error element in the response body, unless
       otherwise negotiated by the request.  In a 207 Multi-Status
       response, this element would appear in the appropriate
       DAV:response-description element.
  
  
  1.6.1Example - CHECKOUT request with DAV:must-not-be-checked-out
       response
  
       >>REQUEST
  
         CHECKOUT /foo.html HTTP/1.1
         Host: www.webdav.org
  
       >>RESPONSE
  
         HTTP/1.1 409 Conflict
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:error xmlns:D="DAV:">
           <D:must-not-be-checked-out/>
         </D:error>
  
       In this example, the request to CHECKOUT /foo.html fails because
       /foo.html is already checked out.
  
  
  1.7 Clarification of COPY Semantics with Overwrite:T
  
       RFC 2518, Section 8.8.4 states:
  
       "If a resource exists at the destination and the Overwrite header
       is "T" then prior to performing the copy the server MUST perform a
       DELETE with "Depth: infinity" on the destination resource."
  
       The purpose of this sentence is to ensure that following a COPY,
       all destination resources have the same content and dead properties
       as the corresponding resources identified by the request-URL (where
       a resources with a given name relative to the Destination URL
       "corresponds" to a resource with the same name relative to the
       request-URL).  If at the time of the request, there already is a
       resource at the destination that has the same resource type as the
       corresponding resource at the request-URL, that resource MUST NOT
       be deleted, but MUST be updated to have the content and dead
       properties of its corresponding member.  If a client wishes all
       resources at the destination to be deleted prior to the COPY, it
       MUST explicitly issue a DELETE request.
  
       The difference between updating a resource and replacing a resource
       with a new resource is especially important when resource history
       is being maintained (the former adds to an existing history, while
  
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       the latter creates a new history).  In addition, locking and access
       control constraints might allow you to update a resource, but not
       allow you to delete it and create a new one in its place.
  
       Note that this clarification does not apply to a MOVE request.  A
       MOVE request with Overwrite:T MUST perform the DELETE with
       "Depth:infinity" on the destination resource prior to performing
       the MOVE.
  
  
  1.8 Versioning Methods and Write Locks
  
       If a write-locked resource has a non-computed property defined by
       this document, the property value MUST NOT be changed by a request
       unless the appropriate lock token is included in the request.
       Since every method introduced in this document other than REPORT
       modifies at least one property defined by this document, every
       versioning method other than REPORT is affected by a write lock. In
       particular, the method MUST fail with a 423 (Locked) status if the
       resource is write-locked and the appropriate token is not specified
       in an If request header.
  
  
  2  BASIC VERSIONING FEATURES
  
       Each basic versioning feature defines extensions to existing HTTP
       and WebDAV methods, as well as new resource types, live properties,
       and methods.
  
  
  2.1 Basic Versioning Packages
  
       Although a server MAY support any combination of versioning
       features, in order to minimize the complexity of a WebDAV basic
       versioning client, a WebDAV basic versioning server SHOULD support
       one of the following three "packages" (feature sets):
  
       - Core-Versioning Package: version-control
       - Basic-Server-Workspace Package: version-control, workspace,
       version-history, checkout
       - Basic-Client-Workspace Package: version-control, working-
       resource, update, label
  
       The core-versioning package supports linear versioning by both
       versioning-aware and versioning-unaware client.  A versioning-aware
       client can use reports and properties to access previous versions
       of a version-controlled resource.
  
       The basic workspace packages support parallel development of
       version-controlled resources.  Each client has its own
       configuration of the shared version-controlled resources, and can
       make changes to its configuration without disturbing that of
       another client.
  
  
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       In the basic-server-workspace package, all persistent state is
       maintained on the server.  Each client has its own workspace
       resource allocated on the server, where each workspace identifies a
       configuration of the shared version-controlled resources.  Each
       client makes changes to its workspace, and can transfer changes
       when appropriate from one workspace to another.  The server
       workspace package is appropriate for clients with no local
       persistent state, or for clients that wish to expose their working
       configurations to other clients.
  
       In the basic-client-workspace package, each client maintains in
       local persistent storage the state for its configuration of the
       shared version-controlled resources.  When a client is ready to
       make its changes visible to other clients, it allocates a set of
       "working resources" on the server, updates the content and dead
       properties of these working resources, and then uses the set of
       working resources to update the version-controlled resources.  The
       working resources are used instead of directly updating the
       version-controlled resources so that sets of consistent updates can
       be prepared in parallel by multiple clients.  Also, a working
       resource allows a client to prepare a single update that requires
       multiple server requests (e.g. updating both the content and dead
       properties of a resource requires both a PUT and a PROPPATCH).  The
       client workspace package simplifies the server implementation by
       requiring each client to maintain its own namespace, but this
       requires that the clients have local persistent state, and does not
       allow clients to expose their working configurations to other
       clients.
  
       A server that supports both basic workspace packages will
       interoperate with all basic versioning clients.
  
  
  2.2 Basic Versioning Semantics
  
  
  2.2.1Creating a Version-Controlled Resource
  
       In order to track the history of the content and dead properties of
       a versionable resource, an author can put the resource under
       version control with a VERSION-CONTROL request.  A VERSION-CONTROL
       request performs three distinct operations:
  
       1) It creates a new "version history resource".  In basic
       versioning, a version history resource is not assigned a URL, and
       hence is not visible in the http scheme URL space.  However, when
       the version-history feature (see Section 5) is supported, this
       changes, and each version history resource is assigned a new
       distinct and unique server-defined URL.
  
       2) It creates a new "version resource" and adds it to the new
       version history resource.  The body and dead properties of the new
       version resource are a copy of those of the versionable resource.
  
  
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       The server assigns the new version resource a new distinct and
       unique URL.
  
       3) It converts the versionable resource into a "version-controlled
       resource".  The version-controlled resource continues to be
       identified by the same URL that identified it as a versionable
       resource.  As part of this conversion, it adds a DAV:checked-in
       property, whose value contains the URL of the new version resource.
  
       Note that a versionable resource and a version-controlled resource
       are not new types of resources (i.e. they introduce no new
       DAV:resourcetype), but rather are any type of resource that
       supports the methods and live properties defined for them in this
       document, in addition to all the methods and live properties
       implied by their DAV:resourcetype.  For example, a collection
       (whose DAV:resourcetype is DAV:collection) is a versionable
       resource if it supports the VERSION-CONTROL method, and is a
       version-controlled resource if it supports the version-controlled
       resource methods and live properties.
  
       In the following example, foo.html is a versionable resource that
       is put under version control.  After the VERSION-CONTROL request
       succeeds, there are two additional resources: a new version history
       resource and a new version resource in that version history.  The
       versionable resource is converted into a version-controlled
       resource, whose DAV:checked-in property identifies the new version
       resource.  The content and dead properties of a resource are
       represented by the symbol appearing inside the box for that
       resource (e.g. "S1" in the following example).
  
            ===VERSION-CONTROL==>
  
                      |                       +----+ version
                      |   version-            |    | history
         versionable  |   controlled          +----+ resource
         resource     |   resource              |
         /foo.html    |   /foo.html             |
                      |                         v
           +----+     |     +----+ checked-in +----+ version
           | S1 |     |     | S1 |----------->| S1 | resource
           +----+     |     +----+            +----+ /his/73/ver/1
  
       Thus, whereas before the VERSION-CONTROL request there was only
       one, non-version-controlled resource, after VERSION-CONTROL there
       are three separate, distinct resources, each containing its own
       state and properties: the version-controlled resource, the version
       resource, and the version history resource.  Since the version-
       controlled resource and the version resource are separate, distinct
       resources, when a method is applied to a version-controlled
       resource, it is only applied to that version-controlled resource,
       and is not applied to the version resource that is currently
       identified by the DAV:checked-in property of that version-
       controlled resource.  Although the content and dead properties of a
       checked-in version-controlled resource are required to be the same
  
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       as those of its current DAV:checked-in version, its live properties
       may differ.  An implementation may optimize storage by retrieving
       the content and dead properties of a checked-in version-controlled
       resource from its current DAV:checked-in version rather than
       storing them in the version-controlled resource, but this is just
       an implementation optimization.
  
       Normally, a resource is placed under version control with an
       explicit VERSION-CONTROL request.  A server MAY automatically place
       every new versionable resource under version control.  In this
       case, the resulting state on the server MUST be the same as if the
       client had explicitly applied a VERSION-CONTROL request to the
       versionable resource.
  
       In order to remove a resource from version control, a client can
       COPY the version-controlled resource to a temporary location,
       DELETE the version-controlled resource, and then MOVE the copy from
       the temporary location back to the original URL.  The versions
       created for that resource while it was under version control will
       continue to exist at their server-defined locations.
  
  
  2.2.2Modifying a Version-Controlled Resource
  
       In order to use methods like PUT and PROPPATCH to directly modify
       the content or dead properties of a version-controlled resource,
       the version-controlled resource must first be checked out.  When
       the checked-out resource is checked in, a new version is created in
       the version history of that version-controlled resource.  The
       version that was checked out is remembered as the predecessor of
       the new version.
  
       The DAV:auto-checkout and DAV:auto-checkin properties (see Sections
       3.2.2 and 3.2.3) of a checked-in version-controlled resource
       determines how it responds to a method that attempts to modify its
       content or dead properties.  Possible responses include:
  
       - Fail the request.  The resource requires an explicit CHECKOUT
       request for it to be modified (see Sections 4 and 9.5).
  
       - Automatically checkout the resource, perform the modification,
       and automatically checkin the resource.  This ensures that every
       state of the resource is tracked by the server, but can result in
       an excessive number of versions being created.
  
       - Fail the request unless the resource is write-locked.  If it is
       write-locked, automatically checkout the resource and perform the
       modification.  The resource remains checked-out until the write-
       lock is removed (either explicitly through a subsequent UNLOCK
       request or implicitly through a time-out of the write-lock).  This
       avoids the proliferation of versions that can result if every
       modification creates a new version.
  
  
  
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       - Automatically checkout the resource, perform the modification,
       and then if the resource is not write-locked, automatically checkin
       the resource.  If the resource is write-locked, it remains checked-
       out until the write-lock is removed.  This helps a locking client
       avoid the proliferation of versions, while still allowing a non-
       locking client to update the resource.
  
       - Automatically checkout the resource, perform the modification,
       and then leave the resource checked out.  An explicit CHECKIN
       operation is used to create a new version.  This minimizes the
       number of new versions that will be created by a versioning unaware
       client, but only a versioning aware client can create new versions.
  
       The following diagram illustrates the effect of the
       checkout/checkin process on a version-controlled resource and its
       version history.  The symbol inside a box (S1, S2, S3) represents
       the current content and dead properties of the resource represented
       by that box.  The symbol next to a box (V1, V2, V3) represents the
       URL for that resource.
  
  
              ===checkout==>     ===PUT==>     ===checkin==>
  
  
           /foo.html (version-controlled resource)
  
            +----+    |    +----+    |    +----+    |    +----+
            | S2 |    |    | S2 |    |    | S3 |    |    | S3 |
            +----+    |    +----+    |    +----+    |    +----+
         Checked-In=V2|Checked-Out=V2|Checked-Out=V2|Checked-In=V3
  
  
           /his/73 (version history for /foo.html)
  
           +----+     |   +----+     |   +----+     |   +----+
           | S1 | V1  |   | S1 | V1  |   | S1 | V1  |   | S1 | V1
           +----+     |   +----+     |   +----+     |   +----+
              |       |      |       |      |       |      |
              |       |      |       |      |       |      |
           +----+     |   +----+     |   +----+     |   +----+
           | S2 | V2  |   | S2 | V2  |   | S2 | V2  |   | S2 | V2
           +----+     |   +----+     |   +----+     |   +----+
                      |              |              |      |
                      |              |              |      |
                      |              |              |   +----+
                      |              |              |   | S3 | V3
                      |              |              |   +----+
  
       Note that a version captures only a defined subset of the state of
       a resource.  In particular, a version of a basic resource captures
       its content and dead properties, but not its live properties.
  
  
  
  
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  2.2.3Reporting
  
       Some versioning information about a resource requires that
       parameters be specified along with that request for information.
       Included in basic versioning is the required support for an
       extensible reporting mechanism, which includes a REPORT method as
       well as a live property for determining what reports are supported
       by a particular resource.  The REPORT method is required by
       versioning, but it can be used in non-versioning WebDAV extensions.
  
       To allow a client to query the properties of all versions in the
       version history of a specified version-controlled resource, basic
       versioning provides the DAV:version-tree report (see Section 3.7).
       In advanced versioning, a more powerful version history reporting
       mechanism is provided by applying the DAV:expand-property report
       (see Section 15.1) to a version history resource (see Section 5).
  
  
  3  VERSION-CONTROL FEATURE
  
       A server indicates that it supports the version-control feature by
       including the string "version-control" as a field in the DAV header
       in the response to an OPTIONS request.  The version-control feature
       MUST be supported if any other versioning feature is supported.
  
  
  3.1 Additional Resource Properties
  
       The version-control feature introduces the following REQUIRED
       properties for any WebDAV resource.
  
  
  3.1.1DAV:comment
  
       This property is used to track a brief comment about a resource
       that is suitable for presentation to a user.  The DAV:comment of a
       version can be used to indicate why that version was created.
  
       <!ELEMENT comment (#PCDATA)>
       PCDATA value: string
  
  3.1.2DAV:creator-displayname
  
       This property contains a description of the creator of the resource
       that is suitable for presentation to a user.  The DAV:creator-
       displayname of a version can be used to indicate who created that
       version.
  
       <!ELEMENT creator-displayname (#PCDATA)>
       PCDATA value: string
  
  
  
  
  
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  3.1.3DAV:supported-method-set (protected)
  
       This property identifies the methods that are supported by the
       resource.
  
       <!ELEMENT supported-method-set (supported-method*)>
       <!ELEMENT supported-method ANY>
       <!ATTLIST supported-method name NMTOKEN #REQUIRED>
       name value: a method name
  
  3.1.4DAV:supported-live-property-set (protected)
  
       This property identifies the live properties that are supported by
       the resource.
  
       <!ELEMENT supported-live-property-set (supported-live-property*)>
       <!ELEMENT supported-live-property ANY>
       <!ATTLIST supported-live-property name NMTOKEN #REQUIRED>
       name value: a property element type
       <!ATTLIST supported-live-property namespace NMTOKEN "DAV:">
       namespace value: an XML namespace
  
  3.1.5DAV:supported-report-set (protected)
  
       This property identifies the reports that are supported by the
       resource.
  
       <!ELEMENT supported-report-set (supported-report*)>
       <!ELEMENT supported-report ANY>
       <!ATTLIST supported-report name NMTOKEN #REQUIRED>
       name value: a property element type
       <!ATTLIST supported-report namespace NMTOKEN "DAV:">
       namespace value: an XML namespace
  
  3.2 Version-Controlled Resource Properties
  
       The version-control feature introduces the following REQUIRED
       properties for a version-controlled resource.
  
  
  3.2.1DAV:checked-in (protected)
  
       This property appears on a checked-in version-controlled resource,
       and identifies a version that has the same content and dead
       properties as the version-controlled resource.  This property is
       removed when the resource is checked out, and then added back
       (identifying a new version) when the resource is checked back in.
  
       <!ELEMENT checked-in (href)>
  
  
  
  
  
  
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  3.2.2DAV:auto-checkout
  
       When a modification request (such as PUT/PROPPATCH) is applied to a
       checked-in version-controlled resource, if the resource is non-
       write-locked and the DAV:auto-checkout property is DAV:unlocked-
       update, or if the resource is write-locked and the DAV:auto-
       checkout property is DAV:locked-update, the request is
       automatically preceded by a checkout operation.
  
       A server MAY refuse to allow the value of the DAV:auto-checkout
       property to be modified.
  
       <!ELEMENT auto-checkout ANY>
       ANY value: A sequence of elements with at most one DAV:unlocked-
       update element and at most one DAV:locked-update element.
       <!ELEMENT unlocked-update EMPTY>
       <!ELEMENT locked-update EMPTY>
  
  3.2.3DAV:auto-checkin
  
       When a modification request (such as PUT/PROPPATCH) on a checked-in
       version-controlled resource has been automatically preceded by a
       checkout operation, if the resource is non-write-locked and the
       DAV:auto-checkin property is DAV:unlocked-update, or if the
       resource is write-locked and the DAV:auto-checkin property is
       DAV:locked-update, the request is automatically followed by a
       checkin operation.
  
       If a write-locked version-controlled resource was automatically
       checked out because the DAV:auto-checkout property was DAV:locked-
       update, and if the resource was still checked-out when the write
       lock is removed (such as from an UNLOCK or lock timeout), then the
       removal of the write lock is automatically preceded by a checkin
       operation.
  
       A server MAY refuse to allow the value of the DAV:auto-checkin
       property to be modified.
  
       <!ELEMENT auto-checkin ANY>
       ANY value: A sequence of elements with at most one DAV:unlocked-
       update element and at most one DAV:locked-update element.
       <!ELEMENT unlocked-update EMPTY>
       <!ELEMENT locked-update EMPTY>
  
  3.3 Checked-Out Resource Properties
  
       The version-control feature introduces the following REQUIRED
       properties for a checked-out resource.
  
  
  
  
  
  
  
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  3.3.1DAV:checked-out (protected)
  
       This property identifies the version that was identified by the
       DAV:checked-in property at the time the resource was checked out.
       When the resource is checked in, this property is removed.
  
       <!ELEMENT checked-out (href)>
  
  
  3.3.2DAV:predecessor-set
  
       This property determines the DAV:predecessor-set property of the
       version that results from checking in this resource.
  
       A server MAY reject attempts to modify the DAV:predecessor-set of a
       version-controlled resource.
  
       <!ELEMENT predecessor-set (href+)>
  
  3.3.3DAV:precursor-set
  
       This property determines the DAV:precursor-set property of the
       version that results from checking in this resource.
  
       <!ELEMENT precursor-set (href*)>
  
  3.4 Version Properties
  
       The version-control feature introduces the following REQUIRED
       properties for a version.
  
  
  3.4.1DAV:predecessor-set (protected)
  
       This property identifies each predecessor of this version.  Except
       for the root version, which has no predecessors, each version has
       at least one predecessor.
  
       <!ELEMENT predecessor-set (href*)>
  
  3.4.2DAV:successor-set (computed)
  
       This property identifies each version whose DAV:predecessor-set
       identifies this version.
  
       <!ELEMENT successor-set (href*)>
  
  3.4.3DAV:checkout-set (computed)
  
       This property identifies each checked-out resource whose
       DAV:checked-out property identifies this version.
  
       <!ELEMENT checkout-set (href*)>
  
  
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  3.4.4DAV:version-name (protected)
  
       This property contains a server-defined string that is different
       for each version in a given version history.  This string is
       intended for display to a user, unlike the URL of a version, which
       is normally only used by a client and not displayed to a user.
  
       <!ELEMENT version-name (#PCDATA)>
       PCDATA value: string
  
  3.4.5DAV:precursor-set (protected)
  
       This property identifies each version from a different version
       history that was copied or merged into the checked-out resource
       that created this version.
  
       <!ELEMENT precursor-set (href*)>
  
  3.5 VERSION-CONTROL Method
  
       A VERSION-CONTROL request can be used to create a version-
       controlled resource at the request-URL.  It can be applied to a
       versionable resource or to a version-controlled resource.
  
       If the request-URL identifies a versionable resource, a new version
       history resource is created, a new version is created whose content
       and dead properties are those of the versionable resource, and the
       resource is given a DAV:checked-in property that is initialized to
       identify this new version.
  
       If the request-URL identifies a version-controlled resource, the
       resource just remains under version-control.  This allows a client
       to be unaware of whether or not a server automatically puts a
       resource under version control when it is created.
  
       If a VERSION-CONTROL request fails, the server state preceding the
       request MUST be restored.
  
     Marshalling:
  
       If a request body is included, it MUST be a DAV:version-control XML
       element.
  
       <!ELEMENT version-control ANY>
  
       The response MUST include a Cache-Control:no-cache header.
  
     Postconditions:
  
       (DAV:put-under-version-control): If the request-URL identified a
       non-null versionable resource at the time of the request, a new
       version history is created and a new version resource is created in
       the new version history.  The resource MUST have a DAV:checked-in
       property that identifies the new version.  The content, dead
  
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       properties, and DAV:resourcetype of the new version MUST be the
       same as those of the resource.  Note that an implementation can
       choose to locate the version history and version resources anywhere
       that it wishes.  In particular, it could locate them on the same
       host and server as the version-controlled resource, on a different
       virtual host maintained by the same server, on the same host
       maintained by a different server, or on a different host maintained
       by a different server.
  
       (DAV:must-not-change-existing-checked-in-out): If the request-URL
       identified a resource already under version control at the time of
       the request, the VERSION-CONTROL request MUST NOT change the
       DAV:checked-in or DAV:checked-out property of that version-
       controlled resource.
  
  
  3.5.1Example - VERSION-CONTROL
  
       >>REQUEST
  
         VERSION-CONTROL /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Cache-Control: no-cache
  
       In this example, /foo.html is put under version control.  A new
       version history is created for it, and a new version is created
       that has a copy of the content and dead properties of /foo.html.
       The DAV:checked-in property of /foo.html identifies this new
       version.
  
  
  3.6 REPORT Method
  
       A REPORT request is an extensible mechanism for obtaining
       information about a resource.  Unlike a resource property, which
       has a single value, the value of a report can depend on additional
       information specified in the REPORT request body and in the REPORT
       request headers.
  
     Marshalling:
  
       The body of a REPORT request specifies which report is being
       requested, as well as any additional information that will be used
       to customize the report.
  
       The request MAY include a Depth header.
  
       The response body for a successful request MUST contain the
       requested report.
  
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       If a Depth request header is included, the response MUST be a 207
       Multi-Status.
  
     Postconditions:
  
       The REPORT method MUST NOT change the content or dead properties of
       any resource.
  
       If a Depth request header is included, the request MUST be applied
       separately to the collection itself and to all members of the
       collection that satisfy the Depth value.  The DAV:prop element of a
       DAV:response for a given resource MUST contain the requested report
       for that resource.
  
  
  3.7 DAV:version-tree REPORT
  
       The DAV:version-tree REPORT describes the requested properties of
       all the versions in the version history of a version.  If the
       report is requested for a version-controlled resource, it is
       redirected to its DAV:checked-in or DAV:checked-out version.
  
     Marshalling:
  
       The request body MUST be a DAV:version-tree XML element.
  
       <!ELEMENT version-tree ANY>
       ANY value: a sequence of zero or more elements, with at most one
       DAV:prop element.
       prop: see RFC 2518, Section 12.11
  
       The response body for a successful request MUST be a
       DAV:multistatus XML element.
  
       multistatus: see RFC 2518, Section 12.9
  
       The response body for a successful DAV:version-tree REPORT request
       MUST contain a DAV:response element for each version in the version
       history of the version identified by the request-URL.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  3.7.1Example - DAV:version-tree REPORT
  
       The version history drawn below would produce the following version
       tree report.
  
  
             foo.html History
  
                  +---+
                  |   | V1
                  +---+
                 /     \
                /       \
            +---+       +---+
            |   | V2    |   | V2.1.1
            +---+       +---+
  
  
       >>REQUEST
  
         REPORT /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:version-tree xmlns:D="DAV:">
           <D:prop>
             <D:version-name/>
             <D:creator-displayname/>
             <D:successor-set/>
           </D:prop>
         </D:version-tree>
  
       >>RESPONSE
  
         HTTP/1.1 207 Multi-Status
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:multistatus xmlns:D="DAV:">
           <D:response>
             <D:href>http://repo.webdav.org/his/23/ver/V1</D:href>
             <D:propstat>
               <D:prop>
                 <D:version-name>V1</D:version-name>
                 <D:creator-displayname>Fred</D:creator-displayname>
                 <D:successor-set>
                   <D:href>http://repo.webdav.org/his/23/ver/V2</D:href>
  
       <D:href>http://repo.webdav.org/his/23/ver/V2.1.1</D:href>
                 </D:successor-set>
  
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               </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
           </D:response>
           <D:response>
             <D:href>http://repo.webdav.org/his/23/ver/V2</D:href>
             <D:propstat>
               <D:prop>
                 <D:version-name>V2</D:version-name>
                 <D:creator-displayname>Fred</D:creator-displayname>
                 <D:successor-set/>
               </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
           </D:response>
           <D:response>
             <D:href>http://repo.webdav.org/his/23/ver/V2.1.1</D:href>
             <D:propstat>
               <D:prop>
                 <D:version-name>V2.1.1</D:version-name>
                 <D:creator-displayname>Sally</D:creator-displayname>
                 <D:successor-set/>
               </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
           </D:response>
         </D:multistatus>
  
  
  3.8 Additional OPTIONS Semantics
  
       If the server supports the version-control feature, it MUST include
       "version-control" as a field in the DAV response header from an
       OPTIONS request on any resource that supports any versioning
       properties, reports, or methods.
  
  
  3.9 Additional PUT Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-modify-version-controlled-content): If the request-URL
       identifies a resource with a DAV:checked-in property, the request
       MUST fail unless the DAV:auto-checkout property of the resource is
       DAV:unlocked-update and the resource is not write-locked, or the
       DAV:auto-checkout property is DAV:locked-update and the resource is
       write-locked.
  
       (DAV:cannot-modify-version): If the request-URL identifies a
       version, the request MUST fail.
  
       If the request creates a new resource that is automatically placed
       under version control, all preconditions for VERSION-CONTROL apply
       to the request.
  
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     Additional Postconditions:
  
       (DAV:auto-checkout): If the resource was a checked-in version-
       controlled resource whose DAV:auto-checkout property indicates it
       should be automatically checked out for a modification request, but
       whose DAV:auto-checkin property does not indicate it should be
       automatically checked in after a modification request, then the
       resource MUST have been automatically checked out prior to
       executing the request.  In particular, the value of the
       DAV:checked-out property of the resource MUST be that of the
       DAV:checked-in property prior to the request, the DAV:checked-in
       property MUST be empty, and the DAV:predecessor-set property MUST
       be initialized to be the same as the DAV:checked-out property.  If
       any part of the checkout/update sequence failed, the status from
       the failed part of the request MUST be returned, and the server
       state preceding the request sequence MUST be restored.
  
        (DAV:auto-version): If the resource was a checked-in version-
       controlled resource whose DAV:auto-checkout property indicates it
       should be automatically checked out for a modification request, and
       whose DAV:auto-checkin property indicates it should be
       automatically checked in after a modification request, then the
       resource MUST have been automatically checked out prior to
       executing the request and automatically checked in after the
       request.  In particular, the DAV:checked-in property of the
       resource MUST identify a new version whose content and dead
       properties are the same as those of the resource.  The
       DAV:predecessor-set of the new version MUST identify the version
       identified by the DAV:checked-in property prior to the request.  If
       any part of the checkout/update/checkin sequence failed, the status
       from the failed part of the request MUST be returned, and the
       server state preceding the request sequence MUST be restored.
  
       If the request creates a new resource, the new resource MAY have
       automatically been placed under version control, and all
       postconditions for VERSION-CONTROL apply to the request.
  
  
  3.10Additional PROPFIND Semantics
  
       A DAV:allprop PROPFIND request SHOULD NOT return any of the
       properties defined by this document.  This allows a versioning
       server to perform efficiently when a naive client, which does not
       understand the cost of asking a server to compute all possible live
       properties, issues a DAV:allprop PROPFIND request.
  
  
  3.11Additional PROPPATCH Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-modify-version-controlled-property): If the request
       attempts to modify a dead property, same semantics as PUT (see
       Section 3.9).
  
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       (DAV:cannot-modify-version): If the request attempts to modify a
       dead property, same semantics as PUT (see Section 3.9).
  
       (DAV:cannot-modify-protected-property): An attempt to modify a
       property defined by this document as being protected for that kind
       of resource MUST fail.
  
       (DAV:cannot-modify-unsupported-property): An attempt to modify a
       property defined by this document whose semantics are not enforced
       by the server MUST fail.  This helps ensure that a client will be
       notified when it is trying to use a property whose semantics are
       not supported by the server.
  
     Additional Postconditions:
  
       (DAV:auto-checkout): If the request modified a dead property, same
       semantics as PUT (see Section 3.9).
  
       (DAV:auto-version): If the request modified a dead property, same
       semantics as PUT (see Section 3.9).
  
  
  3.12Additional DELETE Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-delete-referenced-version): A version that is
       identified in a DAV:checked-in or DAV:checked-out property MUST NOT
       be deleted.
  
       (DAV:no-version-delete): An implementation MAY fail an attempt to
       DELETE a version.
  
     Additional Postconditions:
  
       (DAV:update-predecessor-set): If a version is deleted, any
       reference to that version in a DAV:predecessor-set MUST be replaced
       by a copy of the DAV:predecessor-set of the deleted version.
  
       (DAV:must-be-root-version): If the root version of a version
       history is deleted, there MUST be another version that is the new
       root version, i.e. that is the ancestor of all other versions in
       the version history.
  
  
  3.13Additional COPY Semantics
  
     Additional Preconditions:
  
       If the request creates a new resource that is automatically placed
       under version control, all preconditions for VERSION-CONTROL apply
       to the request.
  
  
  
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     Additional Postconditions:
  
       (DAV:must-not-copy-versioning-property): A property defined by this
       document MUST NOT have been copied to the new resource created by
       this request, but instead that property of the new resource MUST
       have the default initial value it would have had if the new
       resource had been created by a non-versioning method such as PUT or
       a MKCOL.
  
       (DAV:initialize-precursor): If the source of the COPY was a version
       and if the destination of the COPY supports the DAV:precursor-set
       property, the DAV:precursor-set of the destination MUST identify
       that version.  If the source of the COPY was a version-controlled
       resource, the DAV:precursor-set MUST identify the DAV:checked-in or
       DAV:checked-out version of that resource.
  
       (DAV:auto-checkout): If the destination is a version-controlled
       resource, same semantics as PUT (see Section 3.9).
  
       (DAV:auto-version): Same semantics as PUT (see Section 3.9).
  
       The result of copying a version-controlled resource or a version is
       a new non-version-controlled resource at the destination of the
       COPY.  The new resource MAY automatically be put under version
       control, but the resulting version-controlled resource MUST be
       associated with a new version history created for that new version-
       controlled resource, and all postconditions for VERSION-CONTROL
       apply to the request.
  
  
  3.14Additional MOVE Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-rename-resource): If the request-URL identifies a
       version, the request MUST fail.
  
     Additional Postconditions:
  
       (DAV:preserve-versioning-properties): When a resource is moved from
       a source URL to a destination URL, a property defined by this
       document MUST have the same value at the destination URL as it had
       at the source URL.
  
  
  3.15Additional UNLOCK Semantics
  
     Additional Preconditions:
  
       (DAV:version-history-is-tree): If the request-URL identifies a
       version-controlled resource that was automatically checked out
       because its DAV:auto-checkout property was DAV:locked-update, then
       the versions identified by the DAV:predecessor-set of the checked-
  
  
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       out resource MUST be descendants of the root version of the version
       history for the DAV:checked-out version.
  
     Additional Postconditions:
  
       (DAV:create-version): If the request-URL identified a version-
       controlled resource that was automatically checked out because its
       DAV:auto-checkout property was DAV:locked-update, a new version
       MUST have been created in the version history of the DAV:checked-
       out version.  The server MUST allocate a URL for the version that
       MUST NOT have previously identified any other resource, and MUST
       NOT ever identify a resource other than this version.  The content,
       dead properties, DAV:resourcetype, and DAV:predecessor-set of the
       new version MUST be those of the checked-out resource.  The
       DAV:version-name of the new version MUST be set to a server-defined
       value distinct from all other DAV:version-name values of other
       versions in the version history of that version.  The DAV:checked-
       out property of the version-controlled resource MUST have been
       removed, and a DAV:checked-in property that identifies the new
       version MUST have been added.
  
  
  4  CHECKOUT FEATURE
  
       With the version-control feature, WebDAV locking can be used to
       avoid the proliferation of versions that would result if every
       modification to a version-controlled resource produced a new
       version.  The checkout feature provides an alternative mechanism
       that does not require the client to maintain any local state (such
       as a lock token).  Instead, a CHECKOUT method is provided for
       checking out a version-controlled resource, which makes the
       version-controlled resource a checked-out resource.  Also, a
       CHECKIN method is provided for creating a new version by checking
       in a checked-out resource, and an UNCHECKOUT method is provided for
       canceling a checkout and returning the version-controlled resource
       to its state before the checkout.
  
  
  4.1 Additional Version Properties
  
       The checkout feature introduces the following REQUIRED properties
       for a version.
  
  
  4.1.1DAV:checkout-fork
  
       This property controls the behavior of CHECKOUT when a version
       already is checked out or has a successor.  If the DAV:checkout-
       fork of a version is DAV:forbidden, a CHECKOUT request MUST fail if
       it would result in that version appearing in the DAV:predecessor-
       set or DAV:checked-out property of more than one version or
       checked-out resource.  If DAV:checkout-fork is DAV:discouraged,
       such a CHECKOUT request MUST fail unless DAV:fork-ok is specified
       in the CHECKOUT request body.
  
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       A server MAY reject attempts to modify the DAV:checkout-fork of a
       version.
  
       <!ELEMENT checkout-fork ANY>
       ANY value: A sequence of elements with at most one DAV:ok,
       DAV:discouraged, or DAV:forbidden element.
       <!ELEMENT ok EMPTY>
       <!ELEMENT discouraged EMPTY>
       <!ELEMENT forbidden EMPTY>
  
  4.1.2DAV:checkin-fork
  
       This property controls the behavior of CHECKIN when a version
       already has a successor.  If the DAV:checkin-fork of a version is
       DAV:forbidden, a CHECKIN request MUST fail if it would result in
       that version appearing in the DAV:predecessor-set of more than one
       version.  If DAV:checkin-fork is DAV:discouraged, such a CHECKIN
       request MUST fail unless DAV:fork-ok is specified in the CHECKIN
       request body.
  
       A server MAY reject attempts to modify the DAV:checkout-fork of a
       version.
  
       <!ELEMENT checkin-fork ANY>
       ANY value: A sequence of elements with at most one DAV:ok,
       DAV:discouraged, or DAV:forbidden element.
       <!ELEMENT ok EMPTY>
       <!ELEMENT discouraged EMPTY>
       <!ELEMENT forbidden EMPTY>
  
  4.2 CHECKOUT Method
  
       A CHECKOUT request can be applied to a checked-in version-
       controlled resource to allow modifications to the content and dead
       properties of that version-controlled resource.
  
       If a CHECKOUT request fails, the server state preceding the request
       MUST be restored.
  
     Marshalling:
  
       If a request body is included, it MUST be a DAV:checkout XML
       element.
  
       <!ELEMENT checkout ANY>
       ANY value: A sequence of elements with at most one DAV:fork-ok
       element.
  
       <!ELEMENT fork-ok EMPTY>
  
       The response MUST include a Cache-Control:no-cache header.
  
  
  
  
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     Preconditions:
  
       (DAV:must-be-checked-in): If a version-controlled resource is being
       checked out, it MUST have a DAV:checked-in property value.
  
       (DAV:checkout-of-version-with-descendant-is-forbidden): If the
       DAV:checkout-fork property of the version being checked out is
       DAV:forbidden, the request MUST fail if a version identifies that
       version in its DAV:predecessor-set.
  
       (DAV:checkout-of-version-with-descendant-is-discouraged): If the
       DAV:checkout-fork property of the version being checked out is
       DAV:discouraged, the request MUST fail if a version identifies that
       version in its DAV:predecessor-set unless DAV:fork-ok is specified
       in the request body.
  
       (DAV:checkout-of-checked-out-version-is-forbidden): If the
       DAV:checkout-fork property of the version being checked out is
       DAV:forbidden, the request MUST fail if a checked-out resource
       identifies that version in its DAV:checked-out property.
  
       (DAV:checkout-of-checked-out-version-is-discouraged): If the
       DAV:checkout-fork property of the version being checked out is
       DAV:discouraged, the request MUST fail if a checked-out resource
       identifies that version in its DAV:checked-out property unless
       DAV:fork-ok is specified in the request body.
  
     Postconditions:
  
       (DAV:is-checked-out): The checked-out resource MUST have a
       DAV:checked-out property that identifies the DAV:checked-in version
       preceding the checkout.  The version-controlled resource MUST NOT
       have a DAV:checked-in property value.
  
       (DAV:initialize-predecessor-set): The DAV:predecessor-set property
       of the checked-out resource MUST be initialized to be the
       DAV:checked-out version.
  
  
  4.2.1Example - CHECKOUT of a version-controlled resource
  
       >>REQUEST
  
         CHECKOUT /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Cache-Control: no-cache
  
       In this example, the version-controlled resource /foo.html is
       checked out.
  
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  4.3 CHECKIN Method
  
       A CHECKIN request can be applied to a checked-out version-
       controlled resource to produce a new version whose content and dead
       properties are those of the checked-out resource.
  
       If a CHECKIN request fails, the server state preceding the request
       MUST be restored.
  
     Marshalling:
  
       If a request body is included, it MUST be a DAV:checkin XML
       element.
  
       <!ELEMENT checkin ANY>
       ANY value: A sequence of elements with at most one DAV:keep-
       checked-out element and at most one DAV:fork-ok element.
  
       <!ELEMENT keep-checked-out EMPTY>
       <!ELEMENT fork-ok EMPTY>
  
       The response for a successful request MUST include a Location
       header.
  
       The response MUST include a Cache-Control:no-cache header.
  
     Preconditions:
  
       (DAV:must-be-checked-out): The request-URL MUST identify a resource
       with a DAV:checked-out property.
  
       (DAV:version-history-is-tree) The versions identified by the
       DAV:predecessor-set of the checked-out resource MUST be descendants
       of the root version of the version history for the DAV:checked-out
       version.
  
       (DAV:checkin-fork-forbidden): A CHECKIN request MUST fail if it
       would cause a version whose DAV:checkin-fork is DAV:forbidden to
       appear in the DAV:predecessor-set of more than one version.
  
       (DAV:checkin-fork-discouraged): A CHECKIN request MUST fail if it
       would cause a version whose DAV:checkin-fork is DAV:discouraged to
       appear in the DAV:predecessor-set of more than one version, unless
       DAV:fork-ok is specified in the request body.
  
     Postconditions:
  
       (DAV:create-version): A new version MUST have been created in the
       version history of the DAV:checked-out version.  The server MUST
       allocate a distinct new URL for the new version, and that URL MUST
       NOT ever identify any resource other than that version. The URL for
       the new version MUST be returned in a Location response header.
  
  
  
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       (DAV:initialize-version-content-and-properties): The content, dead
       properties, DAV:resourcetype, DAV:predecessor-set, and
       DAV:precursor-set of the new version MUST be those of the checked-
       out resource.  The DAV:version-name of the new version MUST be set
       to a server-defined value distinct from all other DAV:version-name
       values of other versions in the version history of that version.
  
       (DAV:checked-in): If the request-URL identifies a version-
       controlled resource and DAV:keep-checked-out is not specified in
       the request body, the DAV:checked-out property of the version-
       controlled resource MUST have been removed and a DAV:checked-in
       property that identifies the new version MUST have been added.
  
       (DAV:keep-checked-out): If DAV:keep-checked-out is specified in the
       request body, the DAV:checked-out property of the checked-out
       resource MUST have been updated to identify the new version.
  
  
  4.3.1Example - CHECKIN
  
       >>REQUEST
  
         CHECKIN /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 201 Created
         Location: http://repo.webdav.org/his/23/ver/32
         Cache-Control: no-cache
  
       In this example, version-controlled resource /foo.html is checked
       in, and a new version is created at
       http://repo.webdav.org/his/23/ver/32.
  
  
  4.4 UNCHECKOUT Method
  
       An UNCHECKOUT request can be applied to a checked-out version-
       controlled resource to cancel the CHECKOUT and restore the pre-
       CHECKOUT state of the version-controlled resource.  Note that an
       UNCHECKOUT cannot be applied to a working resource (a CHECKOUT that
       created a working resource is canceled by just deleting that
       working resource).
  
       If an UNCHECKOUT request fails, the server state preceding the
       request MUST be restored.
  
     Marshalling:
  
       If a request body is included, it MUST be a DAV:uncheckout XML
       element.
  
  
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       <!ELEMENT uncheckout ANY>
  
       The response MUST include a Cache-Control:no-cache header.
  
     Preconditions:
  
       (DAV:must-be-checked-out-version-controlled-resource): The request-
       URL MUST identify a version-controlled resource with a DAV:checked-
       out property.
  
     Postconditions:
  
       (DAV:cancel-checked-out): The value of the DAV:checked-in property
       is that of the DAV:checked-out property prior to the request, and
       the DAV:checked-out property no longer is set.
  
       (DAV:restore-content-and-dead-properties): The content and dead
       properties of the version-controlled resource are those of its
       DAV:checked-in version.
  
  
  4.4.1Example - UNCHECKOUT
  
       >>REQUEST
  
         UNCHECKOUT /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Cache-Control: no-cache
  
       In this example, the content and dead properties of the version-
       controlled resource identified by http://www.webdav.org/foo.html
       are restored to their values preceding the most recent CHECKOUT of
       that version-controlled resource.
  
  
  4.5 Additional OPTIONS Semantics
  
       If a server supports the checkout feature, it MUST include
       "checkout" as a field in the DAV response header from an OPTIONS
       request on any resource that supports any versioning properties,
       reports, or methods.
  
  
  5  VERSION-HISTORY FEATURE
  
       It is often useful to have access to a version history even after
       all version-controlled resources for that version history have been
       deleted.  A server can provide this functionality by supporting
       version history resources.  A version history resource exists in a
  
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       server defined namespace and therefore is unaffected by any
       deletion or movement of version-controlled resources.  A version
       history resource is an appropriate place to add a property that
       logically applies to all states of a resource.  The DAV:expand-
       property report (see Section 15.1) can be applied to the
       DAV:version-set of a version history resource to provide a variety
       of useful reports on all versions in that version history.
  
  
  5.1 Version History Properties
  
       The DAV:resourcetype of a version history MUST be DAV:version-
       history.
  
       The version-history feature introduces the following REQUIRED
       properties for a version history.
  
  
  5.1.1DAV:version-set (protected)
  
       This property identifies each version of this version history.
  
       <!ELEMENT version-set (href+)>
  
  5.1.2DAV:root-version (computed)
  
       This property identifies the root version of this version history.
  
       <!ELEMENT root-version (href)>
  
  5.2 Additional Version-Controlled Resource Properties
  
       The version-history feature introduces the following REQUIRED
       property for a version-controlled resource.
  
  
  5.2.1DAV:version-history (computed)
  
       This property identifies the version history resource for the
       DAV:checked-in or DAV:checked-out version of this version-
       controlled resource.
  
       <!ELEMENT version-history (href)>
  
  5.3 Additional Version Properties
  
       The version-history feature introduces the following REQUIRED
       property for a version.
  
  
  5.3.1DAV:version-history (computed)
  
       This property identifies the version history that contains this
       version.
  
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       <!ELEMENT version-history (href)>
  
  5.4 DAV:locate-history REPORT
  
       Many properties identify a version from some version history.  It
       is often useful to be able to efficiently locate a version-
       controlled resource for that version history.  The DAV:locate-
       history REPORT can be applied to a collection to locate the
       collection member that is a version-controlled resource for a
       specified version history resource.
  
     Marshalling:
  
       The request body MUST be a DAV:locate-history XML element.
  
       <!ELEMENT locate-history (version-history-set, prop)>
       <!ELEMENT version-history-set (href+)>
       prop: see RFC 2518, Section 12.11
  
       The response body for a successful request MUST be a
       DAV:multistatus XML element containing every version-controlled
       resource that is a member of the collection identified by the
       request-URL, and whose DAV:version-history property identifies one
       of the version history resources identified by the request body.
       The DAV:prop element in the request body identifies which
       properties should be reported in the DAV:prop elements in the
       response body.
  
     Preconditions:
  
       (DAV:must-be-version-history): Each member of the DAV:version-
       history-set element in the request body MUST identify a version
       history resource.
  
  
  5.4.1Example - DAV:locate-history REPORT
  
       >>REQUEST
  
         REPORT /ws/public HTTP/1.1
         Host: www.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:locate-history xmlns:D="DAV:">
           <D:version-history-set>
             <D:href>http://repo.webdav.org/his/23</D:href>
             <D:href>http://repo.webdav.org/his/84</D:href>
             <D:href>http://repo.webdav.org/his/129</D:href>
           </D:version-history-set>
           <D:prop>
             </D:version-history>
           </D:prop>
  
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         </D:locate-history>
  
       >>RESPONSE
  
         HTTP/1.1 207 OK
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:multistatus xmlns:D="DAV:">
           <D:response>
             <D:href>http://www.webdav.org/ws/public/x/test.html</D:href>
             <D:propstat>
               <D:prop>
                 <D:version-history>
                   <D:href>http://repo.webdav.org/his/23</D:href>
                 </D:version-history>
               </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
           </D:response>
         </D:multistatus>
  
       In this example, there is only one version-controlled member of
       /ws/public that is a version-controlled resource for one of the
       three specified version history resources.  In particular,
       /ws/public/x/test.html is the version-controlled resource for
       http://repo.webdav.org/his/23.
  
  
  5.5 Additional OPTIONS Semantics
  
       If the server supports the version-history feature, it MUST include
       "version-history" as a field in the DAV response header from an
       OPTIONS request on any resource that supports any versioning
       properties, reports, or methods.
  
       A DAV:version-history-collection-set element MAY be included in the
       request body to identify collections that may contain version
       history resources.
  
     Additional Marshalling:
  
       If an XML request body is included, it MUST be a DAV:options XML
       element.
  
       <!ELEMENT options ANY>
       ANY value: A sequence of elements with at most one DAV:version-
       history-collection-set element.
  
       If an XML response body for a successful request is included, it
       MUST be a DAV:options-response XML element.
  
       <!ELEMENT options-response ANY>
  
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       ANY value: A sequence of elements with at most one DAV:version-
       history-collection-set element.
  
       <!ELEMENT version-history-collection-set (href*)>
  
       If DAV:version-history-collection-set is included in the request
       body, the response body for a successful request MUST contain a
       DAV:version-history-collection-set element identifying collections
       that may contain version histories.  An identified collection MAY
       be the root collection of a tree of collections, all of which may
       contain version histories.  Since different servers can control
       different parts of the URL namespace, different resources on the
       same host MAY have different DAV:version-history-collection-set
       values.  The identified collections MAY be located on different
       hosts from the resource.
  
  
  5.6 Additional DELETE Semantics
  
     Additional Postconditions:
  
       (DAV:delete-version-set): If a version history is deleted, all
       versions in the DAV:version-set of that version history MUST be
       deleted.
  
       (DAV:must-be-root-version): If the root version of a version
       history is deleted, the DAV:root-version of the version history
       MUST be updated to refer to another version that is an ancestor of
       all other versions in that version history.
  
  
  5.7 Additional COPY Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-copy-history): If the request-URL identifies a version
       history, the request MUST fail.  In order to create another version
       history whose versions have the same content and dead properties,
       the appropriate sequence of VERSION-CONTROL, CHECKOUT, PUT,
       PROPPATCH, and CHECKIN requests must be made.
  
  
  5.8 Additional MOVE Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-rename-resource): If the request-URL identifies a
       version history, the request MUST fail.
  
  
  
  
  
  
  
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  5.9 Additional VERSION-CONTROL Semantics
  
     Additional Postconditions:
  
       (DAV:new-version-history): If the request resulted in the creation
       of a new version history, the server MUST allocate a new server-
       defined URL for that version history that MUST NOT have previously
       identified any other resource, and MUST NOT ever identify a
       resource other than this version history.
  
  
  5.10Additional CHECKIN Semantics
  
     Additional Postconditions:
  
       (DAV:add-to-history): A URL for the new version resource MUST have
       been added to the DAV:version-set of the version history of the
       DAV:checked-out version.
  
  
  6  WORKSPACE FEATURE
  
       In order to allow multiple users to work concurrently on adding
       versions to the same version history, it is necessary to allocate
       on the server multiple checked-out resources for the same version
       history.  Even if only one user is making changes to a resource,
       that user will sometimes wish to create a "private" version, and
       then to expose that version at an appropriate later time.  One way
       to provide this functionality depends on the client keeping track
       of its current set of checked-out resources.  This is the working-
       resource feature defined in Section 8.  The other way to provide
       this functionality avoids the need for persistent state on the
       client, and instead has the server maintain a human meaningful
       namespace for related sets of checked-out resources.  This is the
       workspace feature defined in this section.
  
       The workspace feature introduces a "workspace resource".  A
       workspace resource is a collection whose members are related
       version-controlled and non-version-controlled resources.  In order
       to concurrently expose different versions and configurations of a
       set of version-controlled resources, multiple workspaces may be
       used.  In order to make a change made to a version-controlled
       resource in one workspace visible in another workspace, that
       version-controlled resource must be checked in, and then the
       corresponding version-controlled resource in the other workspace
       can be updated to display the content and dead properties of the
       new version.
  
       In order to ensure unambiguous merging (see Section 7) and
       baselining (see Section 12) semantics, a workspace may contain at
       most one version-controlled resource for a given version history.
       This is required for unambiguous merging because the MERGE method
       must identify which version-controlled resource is to be the merge
       target of a given version.  This is required for unambiguous
  
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       baselining because a baseline can only select one version for a
       given version-controlled resource.
  
       Initially, an empty workspace can be created.  Non-version-
       controlled resources can then be added to the workspace with
       standard WebDAV requests such as PUT and MKCOL.  Version-controlled
       resources can be added to the workspace with VERSION-CONTROL
       requests.  If the baseline feature is supported, collections in the
       workspace can be placed under baseline control, and then
       initialized by existing baselines.
  
  
  6.1 Workspace Properties
  
       The workspace feature introduces the following REQUIRED property
       for a workspace.
  
  
  6.1.1DAV:workspace-checkout-set (computed)
  
       This property identifies each checked-out resource whose
       DAV:workspace property identifies this workspace.
  
       <!ELEMENT workspace-checkout-set (href*)>
  
  6.2 Additional Resource Properties
  
       The workspace feature introduces the following OPTIONAL property
       for a WebDAV resource.
  
  
  6.2.1DAV:workspace (protected)
  
       If the resource is associated with a workspace, this property MUST
       identify this workspace.
  
       <!ELEMENT workspace (href)>
  
       The DAV:workspace property of a workspace MUST identify that
       workspace.  The DAV:workspace property of any other type of
       resource MUST be the same as the DAV:workspace of its parent
       collection.
  
  
  6.3 MKWORKSPACE Method
  
       A MKWORKSPACE request creates a new workspace resource.  A server
       MAY restrict workspace creation to particular collections, but a
       client can determine the location of these collections from a
       DAV:workspace-collection-set OPTIONS request.
  
       If a MKWORKSPACE request fails, the server state preceding the
       request MUST be restored.
  
  
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     Marshalling:
  
       If a request body is included, it MUST be a DAV:mkworkspace XML
       element.
  
       <!ELEMENT mkworkspace ANY>
  
       The response MUST include a Cache-Control:no-cache header.
  
     Preconditions:
  
       (DAV:resource-must-be-null): A resource MUST NOT exist at the
       request-URL.
  
       (DAV:workspace-location-ok): The request-URL MUST identify a
       location where a workspace can be created.
  
     Postconditions:
  
       (DAV:initialize-workspace): A new workspace exists at the request-
       URL.  The DAV:resourcetype of the workspace MUST be DAV:collection.
       The DAV:workspace of the workspace MUST identify the workspace.
  
  
  6.3.1Example - MKWORKSPACE
  
       >>REQUEST
  
         MKWORKSPACE /ws/public HTTP/1.1
         Host: www.webdav.org
         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 201 Created
         Cache-Control: no-cache
  
       In this example, a new workspace is created at
       http://www.webdav.org/ws/public.
  
  
  6.4 Additional OPTIONS Semantics
  
       If a server supports the workspace feature, it MUST include
       "workspace" as a field in the DAV response header from an OPTIONS
       request on any resource that supports any versioning properties,
       reports, or methods.
  
       If a server supports the workspace feature, it MUST also support
       the checkout feature and the version-history feature.
  
       A DAV:workspace-collection-set element MAY be included in the
       request body to identify collections that may contain workspace
       resources.
  
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     Additional Marshalling:
  
       If an XML request body is included, it MUST be a DAV:options XML
       element.
  
       <!ELEMENT options ANY>
       ANY value: A sequence of elements with at most one DAV:workspace-
       collection-set element.
  
       If an XML response body for a successful request is included, it
       MUST be a DAV:options-response XML element.
  
       <!ELEMENT options-response ANY>
       ANY value: A sequence of elements with at most one DAV:workspace-
       collection-set element.
  
       <!ELEMENT workspace-collection-set (href*)>
  
       If DAV:workspace-collection-set is included in the request body,
       the response body for a successful request MUST contain a
       DAV:workspace-collection-set element identifying collections that
       may contain workspaces.  An identified collection MAY be the root
       collection of a tree of collections, all of which may contain
       workspaces.  Since different servers can control different parts of
       the URL namespace, different resources on the same host MAY have
       different DAV:workspace-collection-set values.  The identified
       collections MAY be located on different hosts from the resource.
  
  
  6.5 Additional DELETE Semantics
  
     Additional Postconditions:
  
       (DAV:delete-workspace-members): If a workspace is deleted, any
       resource that identifies that workspace in its DAV:workspace
       property MUST be deleted.
  
  
  6.6 Additional MOVE Semantics
  
     Additional Postconditions:
  
       (DAV:workspace-member-moved): If the request-URL did not identify a
       workspace, the DAV:workspace of the destination MUST have been
       updated to have the same value as the DAV:workspace of the parent
       collection of the destination.
  
       (DAV:workspace-moved): If the request-URL identified a workspace,
       any reference to that workspace in a DAV:workspace property MUST
       have been updated to refer to the new location of that workspace.
  
  
  
  
  
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  6.7 Additional VERSION-CONTROL Semantics
  
       A VERSION-CONTROL request can be used to create a new version-
       controlled resource for an existing version history.  This allows
       the creation of version-controlled resources for the same version
       history in multiple workspaces.
  
     Additional Marshalling:
  
       <!ELEMENT version-control ANY>
       ANY value: A sequence of elements with at most one DAV:version
       element.
  
       <!ELEMENT version (href)>
  
     Additional Preconditions:
  
       (DAV:cannot-add-to-existing-history): If the request-URL identifies
       a versionable resource or a version-controlled resource, the
       DAV:version-control request body element MUST NOT contain a
       DAV:version element.
  
       (DAV:must-be-version): The DAV:href of the DAV:version element MUST
       identify a version.
  
       (DAV:one-version-controlled-resource-per-history-per-workspace): If
       the DAV:version-control request body specifies a version, and if
       the request-URL is a member of a workspace, then there MUST NOT
       already be a version-controlled member of that workspace whose
       DAV:checked-in or DAV:checked-out property identifies any version
       from the version history of the version specified in the request
       body.
  
     Additional Postconditions:
  
       (DAV:new-version-controlled-resource): If the request-URL
       identified a null resource, a new version-controlled resource
       exists at the request-URL whose content and dead properties are
       initialized by those of the version in the request body, and whose
       DAV:checked-in property identifies that version.
  
  
  6.7.1Example - VERSION-CONTROL (using an existing version history)
  
       >>REQUEST
  
         VERSION-CONTROL /ws/public/bar.html HTTP/1.1
         Host: www.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:version-control xmlns:D="DAV:">
           <D:version>
  
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             <D:href>http://repo.webdav.org/his/12/ver/V3</D:href>
           </D:version>
         </D:version-control>
  
       >>RESPONSE
  
         HTTP/1.1 201 Created
         Cache-Control: no-cache
  
       In this example, the null resource /ws/public/bar.html is put under
       version control, and the content and dead properties of the new
       version-controlled resource are initialized to be the same as those
       of the version identified by http://repo.webdav.org/his/12/ver/V3.
  
  
  7  UPDATE FEATURE
  
       The update feature provides a mechanism for restoring a previous
       state of the version-controlled resource.
  
  
  7.1 UPDATE Method
  
       The UPDATE method modifies the content and dead properties of a
       checked-in version-controlled resource to be those of a specified
       version from the version history of that version-controlled
       resource.
  
     Marshalling:
  
       The request-URL MUST identify the resource to be updated.
  
       The request body MUST be a DAV:update element.
  
       <!ELEMENT update ANY>
       ANY value: A sequence of elements with at most one DAV:version
       element.
       <!ELEMENT version (href)>
  
       The response MUST include a Cache-Control:no-cache header.
  
     Preconditions:
  
       (DAV:must-be-checked-in-version-controlled-resource): The request-
       URL MUST identify a checked-in version-controlled resource.
  
       (DAV:must-select-version-in-same-history): The DAV:version element
       in the request body MUST identify a version in the same version
       history as the DAV:checked-in version of the version-controlled
       resource identified by the request-URL.
  
  
  
  
  
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     Postconditions:
  
       (DAV:update-content-and-dead-properties): The content and dead
       properties of the version-controlled resource MUST be the same as
       those of the version specified by the DAV:version element in the
       request body.
  
       (DAV:update-checked-in-property): The DAV:checked-in property of
       the version-controlled resource MUST contain the value of the
       DAV:version element in the request body.
  
  
  7.1.1Example - UPDATE
  
       >>REQUEST
  
         UPDATE /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:update xmlns:D="DAV:">
           <D:version>
             <D:href>http://repo.webdav.org/his/23/ver/33</D:href>
           </D:version>
         </D:update>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Cache-Control: no-cache
  
       In this example, the content and dead properties of
       http://repo.webdav.org/his/23/ver/33 are copied to the version-
       controlled resource /foo.html, and the DAV:checked-in property of
       /foo.html is updated to refer to
       http://repo.webdav.org/his/23/ver/33.
  
  
  7.2 Additional OPTIONS Semantics
  
       If the server supports the update feature, it MUST include "update"
       as a field in the DAV response header from an OPTIONS request on
       any resource that supports any versioning properties, reports, or
       methods.
  
  
  8  LABEL FEATURE
  
       A version "label" is a string that distinguishes one version of a
       version history from all other versions of that version history.  A
       label can automatically be assigned by a server, or it can be
       assigned by a client in order to provide a meaningful name for that
  
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       version.  A given version label can be assigned to at most one
       version of a given version history, but client assigned labels can
       be reassigned to another version at any time.  Note that although a
       given label can be applied to at most one version from the same
       version history, the same label can be applied to versions from
       different version histories.
  
       For certain methods, if the request-URL identifies a version-
       controlled resource, a label can be specified in a Label request
       header (see Section Error! Reference source not found.) to cause
       the method to be applied to the version selected by that label from
       the version history of that version-controlled resource.
  
       Note that it is hard for a distributed versioning server to support
       labels.  In order to ensure that a label does not get assigned to
       multiple versions of the same version history, only one server
       could assign labels to a given version history.  Otherwise, two
       temporarily disconnected servers that have copies of a version
       history could assign the same label to different versions of that
       version history, resulting in two versions in that version history
       with the same label when the two servers are synchronized.
  
  
  8.1 Additional Version Properties
  
       The label feature introduces the following REQUIRED property for a
       version.
  
  
  8.1.1DAV:label-name-set (protected)
  
       This property contains the labels that currently select this
       version.
  
       <!ELEMENT label-name-set (label-name*)>
       <!ELEMENT label-name (#PCDATA)>
       PCDATA value: string
  
  8.2 LABEL Method
  
       A LABEL request can be applied to a version to modify the labels
       that select that version.  The case of a label name MUST be
       preserved when it is stored and retrieved.  When comparing two
       label names to decide if they match or not, a server SHOULD use a
       case-sensitive octet-by-octet comparison of the two label names.
  
       If a LABEL request is applied to a version-controlled resource, the
       operation MUST be applied to the DAV:checked-in version of that
       version-controlled resource.
  
     Marshalling:
  
       The request body MUST be a DAV:label element.
  
  
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       <!ELEMENT label ANY>
       ANY value: A sequence of elements with at most one DAV:add,
       DAV:set, or DAV:remove element.
  
       <!ELEMENT add (label-name)>
       <!ELEMENT set (label-name)>
       <!ELEMENT remove (label-name)>
       <!ELEMENT label-name (#PCDATA)>
       PCDATA value: string
  
       The request MAY include a Label header.
  
       The request MAY include a Depth header.  Standard depth semantics
       apply, and the request is applied to the collection identified by
       the request-URL and to all members of the collection that satisfy
       the Depth value.  If a Depth header is included and the request
       fails on any resource, the response MUST be a 207 Multi-Status that
       identifies all resources for which the request has failed.
  
       The response MUST include a Cache-Control:no-cache header.
  
     Preconditions:
  
       (DAV:must-not-be-checked-out): If the request-URL identifies a
       version-controlled resource, the version-controlled resource MUST
       NOT be checked out.
  
       (DAV:must-select-version-in-history): If a Label request header is
       included and the request-URL identifies a version-controlled
       resource, the specified label MUST select a version in the version
       history of the version-controlled resource.
  
       (DAV:must-be-new-label): If DAV:add is specified in the request
       body, the specified label MUST NOT currently select a version of
       the version history of that version-controlled resource.
  
       (DAV:label-must-exist): If DAV:remove is specified in the request
       body, the specified label MUST select that version.
  
     Postconditions:
  
       (DAV:add-label): If DAV:add or DAV:set is specified in the request
       body, the specified label selects the version.
  
       (DAV:remove-label): If DAV:remove is specified in the request body,
       the specified label no longer selects any version of the version
       history of the version-controlled resource.
  
  
  8.2.1Example - Setting a label
  
       >>REQUEST
  
         LABEL /foo.html HTTP/1.1
  
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         Host: www.webdav.org
         Content-type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:label xmlns:D="DAV:"> <D:set>
           <D:label-name>default</D:label-name>
         </D:set> </D:label>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Cache-Control: no-cache
  
       In this example, the label "default" is applied to the DAV:checked-
       in version of /foo.html.
  
  
  8.3 Label Header
  
       For certain methods (e.g. GET, PROPFIND), if the request-URL
       identifies a version-controlled resource, a label can be specified
       in a Label request header to cause the method to be applied to the
       version selected by that label from the version history of that
       version-controlled resource.
  
       The value of a label header is the name of a label.  For example,
       the label "release-2.0" is identified by the following header:
  
         Label: release-2.0
  
       A Label header MUST have no effect on a request whose request-URL
       does not identify a version-controlled resource.  In particular, it
       MUST have no effect on a request whose request-URL identifies a
       version or a version history.
  
       A server MUST return an HTTP-1.1 Vary header containing Label in a
       successful response to a cacheable request (e.g. GET, PROPFIND)
       that includes a Label header.
  
  
  8.4 Additional OPTIONS Semantics
  
       If the server supports the label feature, it MUST include "label"
       as a field in the DAV response header from an OPTIONS request on
       any resource that supports any versioning properties, reports, or
       methods.
  
  
  8.5 Additional GET Semantics
  
     Additional Marshalling:
  
       The request MAY include a Label header.
  
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     Additional Preconditions:
  
       (DAV:must-select-version-in-history): If a Label request header is
       included and the request-URL identifies a version-controlled
       resource, the specified label MUST select a version in the version
       history of the version-controlled resource.
  
     Additional Postconditions:
  
       If the request-URL identifies a version-controlled resource and a
       Label request header is included, the response MUST contain the
       content of the specified version rather than that of the version-
       controlled resource.
  
  
  8.6 Additional PROPFIND Semantics
  
     Additional Marshalling:
  
       The request MAY include a Label header.
  
     Additional Preconditions:
  
       (DAV:must-select-version-in-history): If a Label request header is
       included and the request-URL identifies a version-controlled
       resource, the specified label MUST select a version in the version
       history of the version-controlled resource.
  
     Additional Postconditions:
  
       If the request-URL identifies a version-controlled resource and a
       Label request header is included, the response MUST contain the
       properties of the specified version rather than that of the
       version-controlled resource.
  
  
  8.7 Additional COPY Semantics
  
     Additional Marshalling:
  
       The request MAY include a Label header.
  
     Additional Preconditions:
  
       (DAV:must-select-version-in-history): If a Label request header is
       included and the request-URL identifies a version-controlled
       resource, the specified label MUST select a version in the version
       history of the version-controlled resource.
  
     Additional Postconditions:
  
       If the request-URL identifies a version-controlled resource and a
       Label request header is included, the request MUST have copied the
  
  
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       properties and content of the specified version rather than that of
       the version-controlled resource.
  
  
  8.8 Additional CHECKOUT Semantics
  
       If the server supports the working-resource option, a LABEL header
       may be included to check out the version selected by the specified
       label.
  
     Additional Marshalling:
  
       The request MAY include a Label header.
  
     Additional Preconditions:
  
       (DAV:must-select-version-in-history): If a Label request header is
       included and the request-URL identifies a version-controlled
       resource, the specified label MUST select a version in the version
       history of the version-controlled resource.
  
       (DAV:must-not-have-label-and-apply-to-version): If a Label request
       header is included, the request body MUST NOT contain a DAV:apply-
       to-version element.
  
     Additional Postconditions:
  
       If the request-URL identifies a version-controlled resource, and a
       Label request header is included, the CHECKOUT MUST have been
       applied to the version selected by the specified label, and not to
       the version-controlled resource itself.  A new working resource
       MUST have been created and the version-controlled resource MUST
       remain checked in.
  
  
  8.9 Additional UPDATE Semantics
  
       A label can be specified to update the content and dead properties
       of the version-controlled resource to be those of the version
       selected by the specified label from the version history of the
       version-controlled resource identified.
  
     Additional Marshalling:
  
       <!ELEMENT update ANY>
       ANY value: A sequence of elements with at most one DAV:label-name
       or DAV:version element (but not both).
       <!ELEMENT label-name (#PCDATA)>
       PCDATA value: string
  
       The request MAY include a Depth header.
  
  
  
  
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     Additional Preconditions:
  
       (DAV:must-select-version-in-history): If the request includes a
       DAV:label-name element in the request body, the label MUST select a
       version in the version history of the version-controlled resource
       identified by the request-URL.
  
       (DAV:depth-update): If the request includes a Depth header,
       standard depth semantics apply, and the request is applied to the
       collection identified by the request-URL and to all members of the
       collection that satisfy the Depth value.  The request MUST be
       applied to a collection before being applied to any members of that
       collection, since an update of a version-controlled collection
       might change the membership of that collection.
  
     Additional Postconditions:
  
       If a Label request header is included, the content and dead
       properties of the version-controlled resource are updated to be
       those of the version selected by that label.
  
  
  9  WORKING-RESOURCE FEATURE
  
       The working-resource feature provides an alternative to the
       workspace feature for supporting parallel development.  Unlike the
       workspace feature, where the desired configuration of versions and
       checked-out resources is maintained on the server, the working-
       resource feature maintains the configuration on the client. This
       simplifies the server implementation, but does not allow a user to
       access the configuration from clients in different physical
       locations, such as from another office, from home, or while
       traveling.  Another difference is that the workspace feature
       isolates clients from a logical change that involves renaming
       shared resources, until that logical change is complete and tested;
       with the working resource feature, all clients use a common set of
       shared version-controlled resources and every client sees the
       result of a MOVE as soon as it occurs.
  
       If a server supports the working-resource feature but not the
       checkout feature, a CHECKOUT request can only be used to create a
       working resource, and cannot be used to check out a version-
       controlled resource.  If a server supports the checkout feature,
       but not the working-resource feature, a CHECKOUT can only be used
       to change the state of a version-controlled resource from checked-
       in to checked-out.
  
  
  9.1 Working Resource Properties
  
       A working resource is a checked-out resource, and therefore has all
       the properties defined in this document for a checked-out resource.
  
  
  
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  9.2 Additional OPTIONS Semantics
  
       If the server supports the working-resource feature, it MUST
       include "working-resource" as a field in the DAV response header
       from an OPTIONS request on any resource that supports any
       versioning properties, reports, or methods.
  
  
  9.3 Additional COPY Semantics
  
     Additional Postconditions:
  
       The result of copying a working resource is a new non-version-
       controlled resource at the destination of the COPY.  The new
       resource MAY automatically be put under version control, but the
       resulting version-controlled resource MUST be associated with a new
       version history created for that new version-controlled resource.
  
  
  9.4 Additional MOVE Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-rename-resource): If the request-URL identifies a
       working resource, the request MUST fail.
  
  
  9.5 Additional CHECKOUT Semantics
  
       A CHECKOUT request can be applied to a version to create a new
       working resource.  The content and dead properties of the working
       resource are a copy of the version that was checked out.
  
     Additional Marshalling:
  
       <!ELEMENT checkout ANY>
       ANY value: A sequence of elements with at most one DAV:apply-to-
       version element.
  
       <!ELEMENT apply-to-version EMPTY>
  
       The response MAY include a Location header.
  
     Additional Postconditions:
  
       (DAV:create-working-resource): If the request-URL identified a
       version, the Location response header MUST contain the URL of a new
       working resource.  The DAV:checked-out property of the new working
       resource MUST identify the version that was checked out.  The
       content and dead properties of the working resource MUST be the
       same as the content and dead properties of the DAV:checked-out
       version.
  
  
  
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       (DAV:create-working-resource-from-checked-in-version): If the
       request-URL identified a version-controlled resource, and
       DAV:apply-to-version is specified in the request body, the CHECKOUT
       is applied to the DAV:checked-in version of the version-controlled
       resource, and not the version-controlled resource itself.  A new
       working resource is created and the version-controlled resource
       remains checked-in.
  
  
  9.5.1Example - CHECKOUT of a version
  
       >>REQUEST
  
         CHECKOUT /his/12/ver/V3 HTTP/1.1
         Host: repo.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 201 Created
         Location: http://repo.webdav.org/wr/157
         Cache-Control: no-cache
  
       In this example, the version identified by
       http://repo.webdav.org/his/12/ver/V3 is checked out, and the new
       working resource is located at http://repo.webdav.org/wr/157.
  
  
  9.6 Additional CHECKIN Semantics
  
       A CHECKIN request can be applied to a working resource to produce a
       new version whose content and dead properties are a copy of those
       of the working resource.  Note that checking in a working resource
       does not change the content or dead properties of any version-
       controlled resource, therefore an UPDATE or MERGE request must be
       used to update a version-controlled resource with the content and
       dead properties of a version created by checking in a working
       resource.
  
     Additional Postconditions:
  
       (DAV:delete-working-resource): If the request-URL identifies a
       working resource and if DAV:keep-checked-out is not specified in
       the request body, the working resource is deleted.
  
  
  9.6.1Example - CHECKIN of a working resource
  
       >>REQUEST
  
         CHECKIN /wr/157 HTTP/1.1
         Host: repo.webdav.org
         Content-Length: 0
  
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       >>RESPONSE
  
         HTTP/1.1 201 Created
         Location: http://repo.webdav.org/his/23/ver/15
         Cache-Control: no-cache
  
       In this example, the working resource /wr/157 checked in, and a new
       version is created at http://repo.webdav.org/his/23/ver/15.
  
  
  10 ADVANCED VERSIONING FEATURES
  
  
  10.1Rationale
  
       Advanced versioning addresses the problems of parallel development
       and configuration management of multiple sets of interrelated
       resources.  Traditionally, artifacts of software development,
       including requirements, design documents, code, and test cases,
       have been a focus of configuration management.  Web sites,
       comprising multiple inter-linked resources (HTML, graphics, sound,
       CGI, and others), are another class of complex information
       artifacts that benefit from the application of configuration
       management.  The advanced versioning capabilities for coordinating
       concurrent change provide the infrastructure for efficient and
       controlled management of large evolving web sites.
  
  
  10.2Advanced Versioning Terms
  
       The following additional terms are used by the advanced versioning
       features.
  
     Collection
  
       A "collection" is a resource whose state consists of not only
       content and properties, but also a set of named "bindings", where a
       binding identifies what RFC 2518 calls an "internal member" of the
       collection.  Note that a binding is not a resource, but rather is a
       part of the state of a collection that defines a mapping from a
       binding name (a URL segment) to a resource (an internal member of
       the collection).
  
     Collection Version Resource
  
       A "collection version resource", or simply "collection version",
       captures the content, dead properties, and version-controlled
       bindings of a version-controlled collection (see Section 14).  A
       version-controlled binding is a binding to a version-controlled
       resource.
  
  
  
  
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     Configuration
  
       A "configuration" is a set of resources that consists of a root
       collection and all members (not just internal members) of that root
       collection that are not members of another configuration.  The root
       collection is called the "configuration root", and the members of
       this set are called the "members of the configuration".  Note that
       a collection (which is a single resource) is very different from a
       configuration (which is a set of resources).
  
     Baseline Resource
  
       A "baseline resource", or simply "baseline", of a collection is a
       version of the configuration that is rooted at that collection (see
       Section 12).  In particular, a baseline captures the DAV:checked-in
       version of every version-controlled member of that configuration.
       Note that a collection version (which captures the state of a
       single resource) is very different from a collection baseline
       (which captures the state of a set of resources).
  
     Baseline-Controlled Collection
  
       A "baseline-controlled collection" is a collection from which
       baselines can be created (see Section 12).
  
     Version-Controlled Configuration Resource
  
       A "version-controlled configuration resource", or simply "version-
       controlled configuration", is a special kind of version-controlled
       resource that is associated with a baseline-controlled collection,
       and is used to create and access baselines of that collection (see
       Section 12).  When a collection is both version-controlled and
       baseline-controlled, a client can create a new version of the
       collection by checking out and checking in that collection, while
       it can create a new baseline of that collection by checking out and
       checking in the version-controlled configuration of that
       collection.
  
     Activity Resource
  
       An "activity resource", or simply "activity", is a non-versionable
       resource that selects a set of versions that correspond to a single
       logical change, where the versions selected from a given version
       history form a single line of descent through that version history
       (see Section 13).
  
  
  10.3Advanced Versioning Packages
  
       Although a server MAY support any combination of advanced
       versioning features, in order to minimize the complexity of a
       WebDAV advanced versioning client, a WebDAV advanced versioning
       server SHOULD support one of the following packages:
  
  
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       Advanced-Server-Workspace Package: Basic-Server-Workspace package
       plus all advanced features
  
       Advanced-Client-Workspace Package: Basic-Client-Workspace Package
       plus all advanced features
  
       The advanced-server-workspace package supports advanced versioning
       capabilities for a client with no persistent state.  The advanced-
       client-workspace package supports advanced versioning capabilities
       for a client that maintains configuration state on the client.  A
       server that supports both advanced workspace packages will
       interoperate with all versioning clients.
  
  
  11 MERGE FEATURE
  
       When an author wants to accept the changes (new versions) created
       by someone else, it is important not to just update the version-
       controlled resources in the author's workspace with those new
       versions, since this could result in "backing out" changes the
       author has made to those version-controlled resources.  Instead,
       the versions created in another workspace should be "merged" into
       the author's version-controlled resources.
  
       The version history of a version-controlled resource provides the
       information needed to determine what should be the result of the
       merge.  In particular, the merge should select whichever version is
       later in the line of descent from the root version.  In case the
       versions to be merged are on different lines of descent (neither
       version is a descendant of the other), neither version should be
       selected, but instead, a new version should be created that
       contains the logical merge of the content and dead properties of
       those versions.  The MERGE request can be used to check out each
       version-controlled resource with such a conflict, and set the
       DAV:merge-set property of each checked-out resource to identify the
       version to be merged.  The author is responsible for modifying the
       content and dead properties of the checked-out resource so that it
       represents the logical merge of that version, and then adding that
       version to the DAV:predecessor-set of the checked-out resource.
  
       If the server is capable of automatically performing the merge, it
       MAY update the content, dead properties, and DAV:predecessor-set of
       the checked-out resource itself.  Before checking in the
       automatically merged resource, the author is responsible for
       verifying that the automatic merge is correct.
  
  
  11.1Additional Checked-Out Resource Properties
  
       The merge feature introduces the following REQUIRED properties for
       a checked-out resource.
  
  
  
  
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  11.1.1    DAV:merge-set
  
       This property identifies each version that is to be merged into
       this checked-out resource.
  
       <!ELEMENT merge-set (href*)>
  
  11.1.2    DAV:auto-merge-set
  
       This property of identifies each version that the server has merged
       into this checked-out resource.  The client should confirm that the
       merge has been performed correctly before moving a URL from the
       DAV:auto-merge-set to the DAV:predecessor-set of a checked-out
       resource.
  
       <!ELEMENT auto-merge-set (href*)>
  
  11.2MERGE Method
  
       The MERGE method performs a logical merge of a specified version
       into a specified version-controlled resource.  If the specified
       version is neither an ancestor nor a descendant of the DAV:checked-
       in or DAV:checked-out version of the version-controlled resource,
       the MERGE checks out the version-controlled resource (if it is not
       already checked out) and adds the URL of the specified version to
       the DAV:merge-set of the version-controlled resource.  It is then
       the client's responsibility to update the content and dead
       properties of the checked-out resource so that it reflects the
       logical merge of the specified version into the current state of
       the version-controlled resource.  The client indicates that it has
       completed the update of the version-controlled resource, by
       deleting the version URL from the DAV:merge-set of the checked-out
       resource, and adding it to the DAV:predecessor-set.  As an error
       check for a client forgetting to complete a merge, the server MUST
       fail an attempt to CHECKIN a version-controlled resource with a
       non-empty DAV:merge-set.
  
       When a server has the ability to automatically update the content
       and dead properties of the version-controlled resource to reflect
       the logical merge of the specified version, it may do so unless
       DAV:no-auto-merge is specified in the MERGE request body.  In order
       to notify the client that a version has been automatically merged,
       the MERGE request MUST add the URL of the auto-merged version to
       the DAV:auto-merge-set property of the version-controlled resource,
       and not to the DAV:merge-set property.  The client indicates that
       it has verified that the auto-merge is valid, by deleting the
       version URL from the DAV:auto-merge-set, and adding it to the
       DAV:predecessor-set.
  
       In general, a MERGE request identifies a "merge source" that
       specifies a set of versions (the "merge versions") and a "merge
       destination" that specifies a set of version-controlled resources
       (the "merge targets").  The set of merge versions is determined as
       follows:
  
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       - If the merge source is a version, that version is the merge
       version.
       - If the merge source is a version-controlled resource, the
       DAV:checked-in version of that version-controlled resource is the
       merge version.
       - If the merge source is a collection, the DAV:checked-in version
       of each version-controlled resource in that collection (as well as
       the DAV:checked-in version of the collection if it is version-
       controlled) is a merge version.
  
       For each merge version, the server determines the "merge target"
       for that merge version.  The merge target is the member of the
       merge destination that is a version-controlled resource whose
       DAV:checked-in or DAV:checked-out version is from the same version
       history as the merge version.  If a merge version has no merge
       target, that merge version is reported by the MERGE as having been
       ignored.
  
     Marshalling:
  
       The merge destination is identified by the request-URL.
  
       The merge source is identified by the DAV:source element in the
       request body.
  
       The request body MUST be a DAV:merge element.
  
       <!ELEMENT merge ANY>
       ANY value: A sequence of elements with one DAV:source element, at
       most one DAV:no-auto-merge element, at most one DAV:no-checkout
       element, at most one DAV:prop element, and any legal set of
       elements that can occur in a DAV:checkout element.
       <!ELEMENT source (href)>
       <!ELEMENT no-auto-merge EMPTY>
       <!ELEMENT no-checkout EMPTY>
       prop: see RFC 2518, Section 12.11
  
       The response body for a successful request MUST be a DAV:merge-
       response element.
  
       <!ELEMENT merge-response ANY>
       ANY value: A sequence of elements with at most one DAV:updated-set
       element, at most one DAV:merged-set element, and at most one
       DAV:ignored-set element.
  
       <!ELEMENT updated-set (response+)>
       <!ELEMENT merged-set (response+)>
       <!ELEMENT ignored-set (href+)>
       response: see RFC 2518, Section 12.9.1
  
       The response MUST include a Cache-Control:no-cache header.
  
  
  
  
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     Preconditions:
  
       (DAV:cannot-merge-checked-out-resource): The DAV:source element
       MUST NOT identify a checked-out resource.  If the DAV:source
       element identifies a collection, the collection MUST NOT have a
       member that is a checked-out resource.
  
       The checkouts performed to resolve conflicts MUST NOT violate any
       of the pre-conditions of the CHECKOUT operation.
  
       (DAV:checkout-not-allowed): If DAV:no-checkout is specified in the
       request body, it MUST be possible to perform the merge without
       checking out any of the merge targets.
  
     Postconditions:
  
       (DAV:ancestor-version): If the merge target is a version-controlled
       resource whose DAV:checked-in version or DAV:checked-out version is
       a descendant of the merge version, the merge target MUST NOT have
       been modified by the MERGE.
  
       (DAV:descendant-version): If the merge target was a checked-in
       version-controlled resource whose DAV:checked-in version was an
       ancestor of the merge version, an UPDATE request MUST have been
       applied to the merge target to set its content and dead properties
       to be those of the merge version, and the merge target MUST appear
       in the DAV:updated-set XML element in the response body.  If the
       UPDATE method is not supported, the merge target MUST have been
       checked out, the content and dead properties of the merge target
       MUST have been set to those of the merge version, the merge version
       MUST have been added to the DAV:auto-merge-set of the merge target,
       and the merge target MUST appear in the DAV:merged-set.
  
       (DAV:checked-out-for-merge): If the merge target was a checked-in
       version-controlled resource whose DAV:checked-in version was
       neither a descendant nor an ancestor of the merge version, a
       CHECKOUT MUST have been applied to the merge target.  All XML
       elements in the DAV:merge XML element that could appear in a
       DAV:checkout XML element MUST have been used as arguments to the
       CHECKOUT request.
  
       (DAV:update-merge-set): If the merge target was checked out by the
       MERGE (or was already checked out before the MERGE), and if the
       DAV:checked-out version of the merge target is not a descendant of
       the merge version, the merge version MUST be added to either the
       DAV:merge-set or the DAV:auto-merge-set of the merge target, and
       the merge target MUST appear in the DAV:merged-set element in the
       response body.  If a merge version has been added to the DAV:auto-
       merge-set, the content and dead properties of the merge target MUST
       have been modified by the server to reflect the result of a logical
       merge of the merge version and the merge target.  If a merge
       version has been added to the DAV:merge-set, the content and dead
       properties of the merge target MUST NOT have been modified by the
  
  
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       server.  If DAV:no-auto-merge is specified in the request body, the
       merge version MUST NOT have been added to the DAV:auto-merge-set.
  
       (DAV:report-ignored-set): If a merge version has no merge target, a
       URL for the merge version MUST appear in the DAV:ignored-set.
  
       (DAV:report-properties): If DAV:prop is specified in the request
       body, the properties specified in the DAV:prop element MUST be
       reported in the DAV:response elements in the DAV:updated-set and
       DAV:merged-set.
  
  
  11.2.1    Example - MERGE
  
       >>REQUEST
  
         MERGE /ws/public HTTP/1.1
         Host: www.webdav.org
         Content-type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:merge xmlns:D="DAV:">
           <D:source>
             <D:href>http://www.webdav.org/ws/dev/sally</D:href>
           </D:source>
         </D:merge>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
         Cache-Control: no-cache
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:merge-response xmlns:D="DAV:">
           <D:update-set>
             <D:href>
               http://www.webdav.org/ws/public/src/parse.c
             </D:href>
             <D:href>
               http://www.webdav.org/ws/public/doc/parse.html
             </D:href>
           </D:update-set>
           <D:ignore-set>
             <D:href>http://repo.webdav.org/his/23/ver/42</D:href>
           </D:ignore-set>
         </D:merge-response>
  
       In this example, the DAV:checked-in versions from the workspace
       http://www.webdav.org/ws/dev/sally are merged into the version-
       controlled resources in the workspace
  
  
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       http://www.webdav.org/ws/public.  Two resources in the workspace
       were updated, and one version was ignored.
  
  
  11.3DAV:merge-preview REPORT
  
       A merge preview describes the changes that would result if the
       versions specified by the DAV:source element in the request body
       were to be merged into the resource identified by the request-URL
       (commonly, a collection).
  
     Marshalling:
  
       The request body MUST be a DAV:merge-preview XML element.
  
       <!ELEMENT merge-preview (source)>
       <!ELEMENT source (href)>
  
       The response body for a successful request MUST be a DAV:merge-
       preview-response XML element.
  
       <!ELEMENT merge-preview-response
        (update-preview | conflict | ignore-preview)*>
  
       A DAV:update-preview element identifies a merge target whose
       DAV:checked-in property would change as a result of the MERGE, and
       identifies the merge version for that merge target.
  
       <!ELEMENT update-preview (target, version)>
       <!ELEMENT target (href)>
       <!ELEMENT version (href)>
  
       A DAV:conflict element identifies a merge target that requires a
       merge.
  
       <!ELEMENT conflict (target, common-ancestor, version)>
  
       A DAV:common-ancestor element identifies the version that is a
       common ancestor of both the merge version and the DAV:checked-in or
       DAV:checked-out version of the merge target.
  
       <!ELEMENT common-ancestor (href)>
  
       A DAV:ignored-preview element identifies a version that has no
       merge target and therefore would be ignored by the merge.
  
       <!ELEMENT ignored-preview (version)>
  
  
  11.3.1    Example - DAV:merge-preview REPORT
  
       >>REQUEST
  
         REPORT /ws/public HTTP/1.1
  
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         Host: www.webdav.org
         Content-type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:merge-preview xmlns:D="DAV:">
           <D:source>
             <D:href>http://www.webdav.org/ws/dev/fred</D:href>
           </D:source>
         </D:merge-preview>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:merge-preview-report xmlns:D="DAV:">
           <D:conflict>
             <D:target>
               <D:href>http://www.webdav.org/ws/public/foo.html</D:href>
             </D:target>
             <D:common-ancestor>
               <D:href>http://repo.webdav.org/his/23/ver/18</D:href>
             </D:common-ancestor>
             <D:version>
               <D:href>http://repo.webdav.org/his/23/ver/42</D:href>
             </D:version>
           </D:conflict>
           <D:update-preview>
             <D:target>
               <D:href>http://www.webdav.org/ws/public/bar.html</D:href>
             </D:target>
             <D:version>
               <D:href>http://www.repo/his/42/ver/3</D:href>
             </D:version>
           </D:update-preview>
         </D:merge-preview-report>
  
       In this example, the merge preview report indicates that version
       /his/23/ver/42 would be merged in /ws/public/foo.html, and version
       /his/42/ver/3 would update /ws/public/bar.html if the workspace
       http://www.webdav.org/ws/dev/fred was merged into the workspace
       http://www.webdav.org/ws/public.
  
  
  11.4Additional OPTIONS Semantics
  
       If the server supports the merge feature, it MUST include "merge"
       as a field in the DAV response header from an OPTIONS request on
       any resource that supports any versioning properties, reports, or
       methods.
  
  
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  11.5Additional DELETE Semantics
  
     Additional Postconditions:
  
       (DAV:delete-version-reference): If a version is deleted, any
       reference to that version in a DAV:merge-set or DAV:auto-merge-set
       property MUST be removed.
  
  
  11.6Additional CHECKIN Semantics
  
     Additional Preconditions:
  
       (DAV:merge-must-be-complete): The DAV:merge-set and DAV:auto-merge-
       set of the checked-out resource MUST be empty.
  
  
  12 BASELINE FEATURE
  
       A "configuration" is a set of resources that consists of a root
       collection and all members of that root collection that are not
       members of another configuration.  A configuration that contains a
       large number of resources can consume a large amount of space on a
       server.  This can make it prohibitively expensive to remember the
       state of an existing configuration by creating a copy of its root
       collection.
  
       A "baseline" is a special kind of version resource that captures
       the state of the version-controlled members of a configuration.  In
       particular, it captures the DAV:checked-in version of each version-
       controlled resource that is a member of the root collection, as
       well as the DAV:checked-in version of the collection if the
       collection itself is a version-controlled resource.  A "baseline
       history" is a special kind of version history whose versions are
       baselines.  New baselines are created by checking out and then
       checking in a special kind of version-controlled resource called a
       "version-controlled configuration".
  
       A collection that is under baseline control is called a "baseline-
       controlled collection".  In order to allow efficient baseline
       implementation, the state of a baseline of a collection is limited
       to be a set of versions and their names relative to the collection,
       and the operations on a baseline are limited to the creation of a
       baseline from a collection, and restoring or merging the baseline
       back into a collection.  A server MAY automatically put a
       collection under baseline control when it is created, or a client
       can use the BASELINE-CONTROL method to put a specified collection
       under baseline control.
  
       As a configuration gets large, it is often useful to break it up
       into a set of smaller configurations that form the logical
       "components" of that configuration.  In order to capture the fact
       that a baseline of a configuration is logically extended by a
  
  
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       component configuration baseline, the component configuration
       baseline is captured as a "subbaseline" of the baseline.
  
       The root directory of a configuration is unconstrained with respect
       to its relationship to the root collection of any of its
       components.  In particular, the root directory of a configuration
       can be an ancestor of a root directory of one of its components
       (e.g. configuration /sys/x can have a component /sys/x/foo), a
       descendant (e.g. configuration /sys/y/z can have a component
       /sys/y), or neither (e.g. configuration /sys/x can have a component
       /comp/bar).
  
  
  12.1Version-Controlled Configuration Properties
  
       Since a version-controlled configuration is a version-controlled
       resource, it has all the properties of a version-controlled
       resource.  In addition, the baseline feature introduces the
       following REQUIRED property for a version-controlled configuration.
  
  
  12.1.1    DAV:baseline-controlled-collection (protected)
  
       This property identifies the collection that contains the version-
       controlled resources whose DAV:checked-in versions are being
       tracked by this version-controlled configuration.  The DAV:version-
       controlled-configuration of the DAV:baseline-controlled-collection
       of a version-controlled configuration MUST identify that version-
       controlled configuration.
  
       <!ELEMENT baseline-controlled-collection (href)>
  
  12.2Checked-Out Configuration Properties
  
       Since a checked-out configuration is a checked-out resource, it has
       all the properties of a checked-out resource.  In addition, the
       baseline feature introduces the following REQUIRED property for a
       checked-out configuration.
  
  
  12.2.1    DAV:subbaseline-set
  
       This property determines the DAV:subbaseline-set property of the
       baseline that results from checking in this resource.
  
       A server MAY reject attempts to modify the DAV:subbaseline-set of a
       checked-out configuration.
  
       <!ELEMENT subbaseline-set (href*)>
  
  12.3Baseline Properties
  
       The DAV:resourcetype of a baseline MUST be DAV:baseline.  Since a
       baseline is a version resource, it has all the properties of a
  
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       version resource.  In addition, the baseline feature introduces the
       following REQUIRED properties for a baseline.
  
  
  12.3.1    DAV:baseline-collection (protected)
  
       This property contains a server-defined URL for a collection of
       checked-in version-controlled resources, where each member of this
       collection has the same DAV:checked-in version and relative name as
       a member of the baseline-controlled collection at the time the
       baseline was created.  At most one member of this collection can
       have a DAV:checked-in version from a given version history.
  
       <!ELEMENT baseline-collection (href)>
  
  12.3.2    DAV:subbaseline-set (protected)
  
       The URLs in the DAV:subbaseline-set property MUST identify a set of
       other baselines.  The subbaselines of a baseline are the baselines
       identified by its DAV:subbaseline-set and all subbaselines of the
       baselines identified by its DAV:subbaseline-set.
  
       <!ELEMENT subbaseline-set (href*)>
  
  12.4Additional Resource Properties
  
       The baseline feature introduces the following OPTIONAL property for
       a resource.
  
  
  12.4.1    DAV:version-controlled-configuration (computed)
  
       If the resource is a member of a version-controlled configuration
       (i.e. the resource is a collection under baseline control or is a
       member of a collection under baseline control), this property
       identifies that version-controlled configuration.
  
       <!ELEMENT version-controlled-configuration (href)>
  
  12.5Additional Workspace Properties
  
       The baseline feature introduces the following REQUIRED property for
       a workspace.
  
  
  12.5.1    DAV:baseline-controlled-collection-set (computed)
  
       This property identifies each member of the workspace that is a
       collection under baseline control (as well as the workspace itself,
       if it is under baseline control).
  
       <!ELEMENT baseline-controlled-collection-set (href*)>
  
  
  
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  12.6BASELINE-CONTROL Method
  
       A collection can be placed under baseline control with a BASELINE-
       CONTROL request.  When a collection is placed under baseline
       control, the DAV:version-controlled-configuration property of the
       collection is set to identify a new version-controlled
       configuration.  This version-controlled configuration can be
       checked out and then checked in to create a new baseline for that
       collection.
  
       If a baseline is specified in the request body, the DAV:checked-in
       version of the new version-controlled configuration will be that
       baseline, and the collection is initialized to contain version-
       controlled members whose DAV:checked-in versions and relative names
       are determined by the specified baseline.
  
       If no baseline is specified, a new baseline history is created, and
       the DAV:checked-in version of the version-controlled configuration
       will be the (empty) root baseline of that baseline history.
  
     Marshalling:
  
       If a request body is included, it MUST be a DAV:baseline-control
       XML element.
  
       <!ELEMENT baseline-control ANY>
       ANY value: A sequence of elements with at most one DAV:baseline
       element.
  
       <!ELEMENT baseline (href)>
  
     Preconditions:
  
       (DAV:version-controlled-configuration-must-be-empty): The
       DAV:version-controlled-configuration property of the collection
       identified by the request-URL MUST be empty.
  
       (DAV:must-be-baseline): The DAV:href of the DAV:baseline element in
       the request body MUST identify a baseline.
  
       (DAV:must-have-no-version-controlled-members): If a DAV:baseline
       element is specified in the request body, the collection identified
       by the request-URL MUST have no members.
  
       (DAV:one-baseline-controlled-collection-per-history-per-workspace):
       If the request-URL identifies a workspace or a member of a
       workspace, and if the DAV:baseline element in the request body
       identifies a baseline history, then there MUST NOT be another
       collection in that workspace whose DAV:version-controlled-
       configuration property identifies a version-controlled
       configuration for that baseline history.
  
  
  
  
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     Postconditions:
  
       (DAV:create-version-controlled-configuration): A new version-
       controlled configuration is created, whose DAV:baseline-controlled-
       collection property identifies the collection.
  
       (DAV:reference-version-controlled-configuration): The DAV:version-
       controlled-configuration of the collection identifies the new
       version-controlled configuration.
  
       (DAV:select-existing-baseline): If the request body specifies a
       baseline, the DAV:checked-in property of the new version-controlled
       configuration MUST have been set to identify this baseline.  A
       version-controlled member of the collection will be created for
       each version in the baseline, where the version-controlled member
       will have the content and dead properties of that version, and will
       have the same name relative to the collection as the corresponding
       version-controlled resource had when the baseline was created.  Any
       nested collections that are needed to provide the appropriate name
       for a version-controlled member will be created.
  
       (DAV:create-empty-baseline): If no baseline is specified in the
       request body, a new baseline history MUST have been created at a
       server-defined URL.  The DAV:baseline-collection of the root
       baseline of the new baseline history MUST identify a collection
       with no members.  The DAV:checked-in property of the new version-
       controlled configuration MUST identify the root baseline of the new
       baseline history.
  
  
  12.6.1    Example - BASELINE-CONTROL
  
       >>REQUEST
  
         BASELINE-CONTROL /src HTTP/1.1
         Host: www.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:baseline-control xmlns:D="DAV:">
           <D:href>http://repo.webdav.org/bl-his/22/bl/17</D:href>
         </D:baseline-control>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
  
       In this example, the collection identified by
       http://www.webdav.org/src is placed under baseline control and is
       initialized with version-controlled members whose DAV:checked-in
       versions are those selected by the baseline identified by
       http://repo.webdav.org/bl-his/22/bl/17.
  
  
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  12.7DAV:compare-baseline REPORT
  
       A DAV:compare-baseline REPORT contains the differences between the
       baseline identified by the request-URL (the "request baseline") and
       the baseline specified in the request body (the "compare
       baseline").
  
     Marshalling:
  
       The request body MUST be a DAV:compare-baseline XML element.
  
       <!ELEMENT compare-baseline (href)>
  
       The response body for a successful request MUST be a DAV:compare-
       baseline-report XML element.
  
       <!ELEMENT compare-baseline-report
        (added-version | deleted-version | changed-version)*>
  
       A DAV:added-version element identifies a version that is the
       DAV:checked-in version of a member of the DAV:baseline-collection
       of the compare baseline, but no version in the version history of
       that version is the DAV:checked-in version of a member of the
       DAV:baseline-collection of the request baseline.
  
       <!ELEMENT added-version (href)>
  
       A DAV:deleted-version element identifies a version that is the
       DAV:checked-in version of a member of the DAV:baseline-collection
       of the request baseline, but no version in the version history of
       that version is the DAV:checked-in version of a member of the
       DAV:baseline-collection of the compare baseline.
  
       <!ELEMENT deleted-version (href)>
  
       A DAV:changed-version element identifies two different versions
       from the same version history that are the DAV:checked-in version
       of the DAV:baseline-collection of the request baseline and the
       compare baseline, respectively.
  
       <!ELEMENT changed-version (href, href)>
  
     Preconditions:
  
       (DAV:must-be-baseline): The DAV:href in the request body MUST
       identify a baseline.
  
       (DAV:baselines-from-same-history): A server MAY require that the
       baselines being compared be from the same baseline history.
  
  
  12.7.1    Example - DAV:compare-baseline REPORT
  
       >>REQUEST
  
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         REPORT /bl-his/12/bl/14 HTTP/1.1
         Host: repo.webdav.com
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:compare-baseline xmlns:D="DAV:">
           <D:href>http://repo.webdav.org/bl-his/12/bl/15</D:href>
         </D:compare-baseline>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:compare-baseline-report xmlns:D="DAV:">
           <D:added-version>
             <D:href>http://repo.webdav.org/his/23/ver/8</D:href>
           </D:added-version>
           <D:changed-version>
             <D:href>http://repo.webdav.org/his/29/ver/12</D:href>
             <D:href>http://repo.webdav.org/his/29/ver/19</D:href>
           </D:changed-version>
           <D:deleted-version>
             <D:href>http://repo.webdav.org/his/12/ver/4</D:href>
           </D:deleted-version>
         </D:compare-baseline-report>
  
       In this example, the differences between baseline 14 and baseline
       15 of http://repo.webdav.org/bl-his/12 are identified.
  
  
  12.8Additional OPTIONS Semantics
  
       If a server supports the baseline feature, it MUST include
       "baseline" as a field in the DAV response header from an OPTIONS
       request on any resource that supports any versioning properties,
       reports, or methods.
  
  
  12.9Additional MKCOL Semantics
  
     Additional Postconditions:
  
       If a server automatically puts a newly created collection under
       baseline control, all postconditions for BASELINE-CONTROL apply to
       the MKCOL.
  
  
  
  
  
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  12.10     Additional COPY Semantics
  
     Additional Postconditions:
  
       If the request creates a new collection at the Destination, and a
       server automatically puts a newly created collection under baseline
       control, all postconditions for BASELINE-CONTROL apply to the COPY.
  
  
  12.11     Additional CHECKOUT Semantics
  
     Additional Preconditions:
  
       (DAV:must-not-update-baseline-collection): If the request-URL
       identifies a member of the configuration rooted at the
       DAV:baseline-collection of a baseline, the request MUST fail.
  
  
  12.12     Additional CHECKIN Semantics
  
     Additional Preconditions:
  
       (DAV:no-checked-out-baseline-controlled-collection-members): If the
       request-URL identifies a version-controlled configuration, all
       version-controlled members of the DAV:baseline-controlled-
       collection of the version-controlled configuration MUST be checked-
       in.
  
       (DAV:one-version-per-history-per-baseline): If the request-URL
       identifies a version-controlled configuration, the set of versions
       selected by that version-controlled configuration MUST contain at
       most one version from any version history, where a version is
       selected by a version-controlled configuration if the version is
       identified by the DAV:checked-in property of any member of the
       configuration rooted at the DAV:baseline-controlled collection of
       that version-controlled configuration, or is identified by the
       DAV:checked-in property of any member of the configuration rooted
       at the DAV:baseline-collection of any subbaseline of that version-
       controlled configuration.
  
       (DAV:cannot-modify-version-controlled-configuration): If the
       request-URL identifies a version-controlled member of a baseline-
       controlled collection, the request MUST fail unless the DAV:auto-
       checkout property of the version-controlled configuration of that
       baseline-controlled collection is DAV:unlocked-update and the
       configuration is not write-locked, or the DAV:auto-checkout
       property is DAV:locked-update and the configuration is write-
       locked.
  
     Additional Postconditions:
  
       (DAV:create-baseline-collection): If the request-URL identifies a
       version-controlled configuration, the DAV:baseline-collection of
       the new baseline identifies a collection whose members have the
  
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       same relative name and DAV:checked-in version as the members of the
       DAV:baseline-controlled-collection of the version-controlled
       configuration at the time of the request.
  
       (DAV:modify-configuration): If the request-URL identifies a
       version-controlled member of a baseline-controlled collection, this
       is a modification to the version-controlled configuration of that
       baseline-controlled collection, and standard auto-versioning
       semantics apply.
  
  
  12.13     Additional UPDATE Semantics
  
     Additional Preconditions:
  
       (DAV:baseline-controlled-members-must-be-checked-in): If the
       request-URL identifies a version-controlled configuration, then all
       version-controlled members of the DAV:baseline-controlled-
       collection of that version-controlled configuration MUST be
       checked-in.
  
       (DAV:must-not-update-baseline-collection): If the request-URL
       identifies a member of the configuration rooted at the
       DAV:baseline-collection of a baseline, the request MUST fail.
  
       (DAV:cannot-modify-version-controlled-configuration): If the
       request updates the DAV:checked-in property of any version-
       controlled member of a baseline-controlled collection, the request
       MUST fail unless the DAV:auto-checkout property of the version-
       controlled configuration of that baseline-controlled collection is
       DAV:unlocked-update and the configuration is not write-locked, or
       the DAV:auto-checkout property is DAV:locked-update and the
       configuration is write-locked.
  
     Additional Postconditions:
  
       (DAV:set-baseline-controlled-collection-members): If the request-
       URL identifies a version-controlled configuration and the
       DAV:version element identifies a baseline, then the version-
       controlled members of the DAV:baseline-controlled-collection of
       that version-controlled configuration MUST have been updated so
       that they have the same relative name, content, and dead properties
       as the members of the DAV:baseline-collection of the baseline.  In
       particular:
       - A version-controlled member for a given version history MUST have
       been deleted if there is no version-controlled member for that
       version history in the DAV:baseline-collection of the baseline.
       - A version-controlled member for a given version history MUST have
       been renamed if its name relative to the baseline-controlled
       collection is different from that of the version-controlled member
       for that version history in the DAV:baseline-collection of the
       baseline.
       - A new version-controlled member MUST have been created for each
       member of the DAV:baseline-collection of the baseline for which
  
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       there is no corresponding version-controlled member in the
       baseline-controlled collection.
       - An UPDATE request MUST have been applied to each version-
       controlled member for a given version history whose DAV:checked-in
       version is not the same as that of the version-controlled member
       for that version history in the DAV:baseline-collection of the
       baseline.
  
       (DAV:modify-configuration): If the request updated the DAV:checked-
       in property of any version-controlled member of a baseline-
       controlled collection, this is a modification to the version-
       controlled configuration of that baseline-controlled collection,
       and standard auto-versioning semantics apply.
  
  
  12.14     Additional MERGE Semantics
  
       If the merge version is a baseline, the merge target is a version-
       controlled configuration for the baseline history of that baseline,
       where the baseline-controlled collection of that version-controlled
       configuration is a member of the merge destination of the request.
  
     Additional Preconditions:
  
       (DAV:must-not-update-baseline-collection): Same as UPDATE (see
       Section 12.13).
  
       (DAV:cannot-modify-version-controlled-configuration): Same as
       UPDATE (see Section 12.13).
  
     Additional Postconditions:
  
       (DAV:merge-baseline): If the merge target is a version-controlled
       configuration whose DAV:checked-out baseline is not a descendant of
       the merge baseline, then the merge baseline MUST have been added to
       the DAV:auto-merge-set of a version-controlled configuration.  Each
       baseline in the DAV:subbaseline-set of that baseline MUST have been
       merged into the merge destination, and the DAV:checked-in version
       of each member of the DAV:baseline-collection of that baseline MUST
       have been merged into the DAV:baseline-controlled-collection of
       that version-controlled configuration.
  
       (DAV:modify-configuration): Same as UPDATE (see Section 12.13).
  
  
  13 ACTIVITY FEATURE
  
       An "activity" is a non-versionable resource that selects a set of
       versions that are on a single "line of descent", where a line of
       descent is a sequence of versions connected by successor
       relationships.  If an activity selects versions from multiple
       version histories, the versions selected in each version history
       must be on a single line of descent.
  
  
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       A common problem that motivates the use of activities is that it is
       often desirable to perform several different logical changes in a
       single workspace, and then selectively merge a subset of those
       logical changes to other workspaces.  An activity can be used to
       represent a single logical change, where an activity tracks all the
       resources that were modified to effect that single logical change.
       When a version-controlled resource is checked out, the author
       specifies which activity should be associated with a new version
       that will be created when that version-controlled resource is
       checked in.  It is then possible to select a particular logical
       change for merging into another workspace, by specifying the
       appropriate activity in a MERGE request.
  
       Another common problem is that although a version-controlled
       resource may need to have multiple lines of descent, all work done
       by members of a given team must be on a single line of descent (to
       avoid merging between team members).  An activity resource provides
       the mechanism for addressing this problem.  When a version-
       controlled resource is checked out, a client can request that an
       existing activity be used or that a new activity be created.
       Activity semantics then ensure that all versions in a given version
       history that are associated with an activity are on a single line
       of descent.  If all members of a team share a common activity (or
       sub-activities of a common activity), then all changes made by
       members of that team will be on a single line of descent.
  
       The following diagram illustrates activities.  Version V5 is the
       latest version of foo.html selected by activity Act-2, and version
       V8 is the latest version of bar.html selected by activity Act-2.
  
  
  
            foo.html History      bar.html History
  
                  +---+                 +---+
             Act-1|   |V1          Act-1|   |V6
                  +---+                 +---+
                    |                     |
                    |                     |
                  +---+                 +---+
             Act-1|   |V2          Act-2|   |V7
                  +---+                 +---+
                 /     \                  |
                /       \                 |
           +---+        +---+           +---+
      Act-1|   |   Act-2|   |V4    Act-2|   |V8
           +---+        +---+           +---+
                          |               |
                          |               |
                        +---+           +---+
                   Act-2|   |V5    Act-3|   |V9
                        +---+           +---+
  
  
  
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       Activities appear under a variety of names in existing versioning
       systems.  When an activity is used to capture a logical change, it
       is commonly called a "change set".  When an activity is used to
       capture a line of descent, it is commonly called a "branch".  When
       a system supports both branches and change sets, it is often useful
       to require that a particular change set occur on a particular
       branch.  This relationship can be captured by making the change set
       activity be a "subactivity" of the branch activity.
  
  
  13.1Activity Properties
  
       The activity feature introduces the following REQUIRED properties
       for an activity.
  
  
  13.1.1    DAV:activity-version-set (computed)
  
       This property identifies each version whose DAV:activity-set
       property identifies this activity.  Multiple versions of a single
       version history can be selected by an activity's DAV:activity-
       version-set property, but all DAV:activity-version-set versions
       from a given version history must be on a single line of descent
       from the root version of that version history.
  
       <!ELEMENT activity-version-set (href*)>
  
  13.1.2    DAV:activity-checkout-set (computed)
  
       This property identifies each checked-out resource whose
       DAV:activity-set identifies this activity.
  
       <!ELEMENT activity-checkout-set (href*)>
  
  13.1.3    DAV:subactivity-set
  
       This property identifies each activity that forms a part of the
       logical change being captured by this activity.  An activity
       behaves as if its DAV:activity-version-set is extended by the
       DAV:activity-version-set of each activity identified in the
       DAV:subactivity-set.  In particular, the versions in this extended
       set MUST be on a single line of descent, and when an activity
       selects a version for merging, the latest version in this extended
       set is the one that will be merged.
  
       A server MAY reject attempts to modify the DAV:subactivity-set of
       an activity.
  
       <!ELEMENT subactivity-set (href*)>
  
  13.1.4    DAV:current-workspace-set (computed)
  
       This property identifies each workspace whose DAV:current-activity-
       set identifies this activity.
  
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       <!ELEMENT current-workspace-set (href*)>
  
  13.2Additional Version Properties
  
       The activity feature introduces the following REQUIRED property for
       a version.
  
  
  13.2.1    DAV:activity-set
  
       This property identifies the activities that determine to which
       logical changes this version contributes, and on which lines of
       descent this version appears.  A server MAY restrict the
       DAV:activity-set to identify a single activity.  A server MAY
       refuse to allow the value of the DAV:activity-set property of a
       version to be modified.
  
       <!ELEMENT activity-set (href*)>
  
  13.3Additional Checked-Out Resource Properties
  
       The activity feature introduces the following REQUIRED properties
       for a checked-out resource.
  
  
  13.3.1    DAV:unreserved
  
       This property of a checked-out resource indicates whether the
       DAV:activity-set of another checked-out resource associated with
       the version history of this version-controlled resource can have an
       activity that is in the DAV:activity-set property of this checked-
       out resource.
  
       A result of the requirement that an activity must form a single
       line of descent through a given version history is that if multiple
       checked-out resources for a given version history are checked out
       unreserved into a single activity, only the first CHECKIN will
       succeed.  Before another of these checked-out resources can be
       checked in, the author will first have to merge into that checked-
       out resource the latest version selected by that activity from that
       version history, and then modify the DAV:predecessor-set of that
       checked-out resource to identify that version.
  
       <!ELEMENT unreserved (#PCDATA)>
       PCDATA value: boolean
  
  13.3.2    DAV:activity-set
  
       This property of a checked-out resource determines the
       DAV:activity-set property of the version that results from checking
       in this resource.
  
  
  
  
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  13.4Additional Workspace Properties
  
       The activity feature introduces the following REQUIRED property for
       a workspace.
  
  
  13.4.1    DAV:current-activity-set
  
       This property identifies the activities that currently are being
       performed in this workspace.  When a member of this workspace is
       checked out, if no activity is specified in the checkout request,
       the DAV:current-activity-set will be used.  This allows an
       activity-unaware client to update a workspace in which activity
       tracking is required.  The DAV:current-activity-set MAY be
       restricted to identify at most one activity.
  
       <!ELEMENT current-activity-set (href*)>
  
  13.5MKACTIVITY Method
  
       A MKACTIVITY request creates a new activity resource.  A server MAY
       restrict activity creation to particular collections, but a client
       can determine the location of these collections from a
       DAV:activity-collection-set OPTIONS request.
  
     Marshalling:
  
       If a request body is included, it MUST be a DAV:mkactivity XML
       element.
  
       <!ELEMENT mkactivity ANY>
  
       The response MUST include a Cache-Control:no-cache header.
  
     Preconditions:
  
       (DAV:resource-must-be-null): A resource MUST NOT exist at the
       request-URL.
  
       (DAV:activity-location-ok): The request-URL MUST identify a
       location where an activity can be created.
  
     Postconditions:
  
       (DAV:initialize-activity): A new activity exists at the request-
       URL.  The DAV:resourcetype of the activity MUST be DAV:activity.
  
  
  13.5.1    Example - MKACTIVITY
  
       >>REQUEST
  
         MKACTIVITY /act/test-23 HTTP/1.1
         Host: repo.webdav.org
  
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         Content-Length: 0
  
       >>RESPONSE
  
         HTTP/1.1 201 Created
         Cache-Control: no-cache
  
       In this example, a new activity is created at
       http://repo.webdav.org/act/test-23.
  
  
  13.6DAV:latest-activity-version REPORT
  
       The DAV:latest-activity-version REPORT can be applied to a version
       history to identify the latest version that is selected from that
       version history by a given activity.
  
     Marshalling:
  
       The request body MUST be a DAV:latest-activity-version XML element.
  
       <!ELEMENT latest-activity-version (href)>
  
       The response body for a successful request MUST be a DAV:latest-
       activity-version-report XML element.
  
       <!ELEMENT latest-activity-version-report (href)>
  
       The DAV:href of the response body MUST identify the version of the
       given version history that is a member of the DAV:activity-version-
       set of the given activity and has no ancestor that is a member of
       the DAV:activity-version-set of the given activity.
  
     Preconditions:
  
       (DAV:must-be-activity): The DAV:href in the request body MUST
       identify an activity.
  
  
  13.7Additional OPTIONS Semantics
  
       If the server supports the activity feature, it MUST include
       "activity" as a field in the DAV response header from an OPTIONS
       request on any resource that supports any versioning properties,
       reports, or methods.
  
       A DAV:activity-collection-set element MAY be included in the
       request body to identify collections that may contain activity
       resources.
  
     Additional Marshalling:
  
       If an XML request body is included, it MUST be a DAV:options XML
       element.
  
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       <!ELEMENT options ANY>
       ANY value: A sequence of elements with at most one DAV:activity-
       collection-set element.
  
       If an XML response body for a successful request is included, it
       MUST be a DAV:options-response XML element.
  
       <!ELEMENT options-response ANY>
       ANY value: A sequence of elements with at most one DAV:activity-
       collection-set element.
  
       <!ELEMENT activity-collection-set (href*)>
  
       If DAV:activity-collection-set is included in the request body, the
       response body for a successful request MUST contain a DAV:activity-
       collection-set element identifying collections that may contain
       activities.  An identified collection MAY be the root collection of
       a tree of collections, all of which may contain activities.  Since
       different servers can control different parts of the URL namespace,
       different resources on the same host MAY have different
       DAV:activity-collection-set values.  The identified collections MAY
       be located on different hosts from the resource.
  
  
  13.8Additional DELETE Semantics
  
     Additional Postconditions:
  
       (DAV:delete-activity-reference): If an activity is deleted, any
       reference to that activity in a DAV:activity-set, DAV:subactivity-
       set, or DAV:current-activity-set MUST be removed.
  
  
  13.9Additional MOVE Semantics
  
     Additional Postconditions:
  
       (DAV:update-checked-out-reference): If a checked-out resource is
       moved, any reference to that resource in a DAV:activity-checkout
       property MUST be updated to refer to the new location of that
       resource.
  
       (DAV:update-activity-reference): If the request-URL identifies an
       activity, any reference to that activity in a DAV:activity-set,
       DAV:subactivity-set , or DAV:current-activity-set MUST be updated
       to refer to the new location of that activity.
  
       (DAV:update-workspace-reference): If the request-URL identifies a
       workspace, any reference to that workspace in a DAV:current-
       workspace-set property MUST be updated to refer to the new location
       of that workspace.
  
  
  
  
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  13.10     Additional CHECKOUT Semantics
  
       A CHECKOUT request MAY specify the DAV:activity-set for the
       checked-out resource.
  
     Additional Marshalling:
  
       <!ELEMENT checkout ANY>
       ANY value: A sequence of elements with at most one DAV:activity-set
       and at most one DAV:unreserved.
  
       <!ELEMENT activity-set (href+ | new)>
       <!ELEMENT new EMPTY>
       <!ELEMENT unreserved EMPTY>
  
     Additional Preconditions:
  
       (DAV:one-checkout-per-activity-per-history): If there is a request
       activity set, unless DAV:unreserved is specified, another checkout
       from a version of that version history MUST NOT select an activity
       in that activity set.
  
       (DAV:linear-activity): If there is a request activity set, unless
       DAV:unreserved is specified, the selected version MUST be a
       descendant of all other versions of that version history that
       select that activity.
  
     Additional Postconditions:
  
       (DAV:initialize-activity-set): The DAV:activity-set of the checked-
       out resource is set as follows:
       - If DAV:new is specified as the DAV:activity-set in the request
       body, then a new activity created by the server is used.
       - Otherwise, if activities are specified in the request body, then
       those activities are used.
       - Otherwise, if the version-controlled resource is a member of a
       workspace and the DAV:current-activity-set of the workspace is set,
       then those activities are used.
       - Otherwise, the DAV:activity-set of the DAV:checked-out version is
       used.
  
       (DAV:initialize-unreserved): If DAV:unreserved was specified in the
       request body, then the DAV:unreserved property of the checked-out
       resource MUST be "true".
  
  
  13.10.1   Example - CHECKOUT with an activity
  
       >>REQUEST
  
         CHECKOUT /ws/public/foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
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         <?xml version="1.0" encoding="utf-8" ?>
         <D:checkout xmlns:D="DAV:">
           <D:activity-set>
             <D:href>http://repo.webdav.org/act/fix-bug-23</D:href>
           </D:activity-set>
         </D:checkout>
  
       >>RESPONSE
  
         HTTP/1.1 200 OK
         Cache-Control: no-cache
  
  
       In this example, the CHECKOUT is being performed in the
       http://repo.webdav.org/act/fix-bug-23 activity.
  
  
  13.11     Additional CHECKIN Semantics
  
     Additional Preconditions:
  
       (DAV:linear-activity): Any version which is in the version history
       of the checked-out resource and whose DAV:activity-set identifies
       an activity from the DAV:activity-set of the checked-out resource
       MUST be an ancestor of the checked-out resource.
  
     Additional Postconditions:
  
       (DAV:initialize-activity-set): The DAV:activity-set of the new
       version MUST have been initialized to be the same as the
       DAV:activity-set of the checked-out resource.
  
  
  13.12     Additional MERGE Semantics
  
       If the DAV:source element of the request body identifies an
       activity, then all checked-out resources in that activity (or any
       subactivity of that activity) are checked in, and then for each
       version history containing a version selected by that activity, the
       latest version selected by that activity is a merge version.  Note
       that the versions selected by an activity are the versions in its
       DAV:activity-version-set unioned with the versions selected by the
       activities in its DAV:subactivity-set.
  
       A checked-out baseline in the activity is checked-in only after all
       other checked-out resources have been checked in and merged to
       their merge target.  This ensures that modifications to members of
       a collection are captured by any new baseline of that collection.
       If a working baseline is checked in, the baseline-controlled
       collection that determines the DAV:baseline-collection of the new
       baseline is the merge target of that working baseline.
  
  
  
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     Additional Preconditions:
  
       (DAV:atomic-activity-checkin): If the DAV:source element identifies
       an activity, the server MAY fail the request if any of the checked-
       out resources in the DAV:activity-checkout-set of the activity
       cannot be checked in.
  
     Additional Postconditions:
  
       (DAV:checkin-activity): If the DAV:source element identified an
       activity, before determining the merge versions, the server MUST
       have checked in each checked-out resource that was in the
       DAV:activity-checkout-set.  Before checking in a checked-out
       baseline, the server MUST have already checked in and merged all
       checked-out non-baseline resources.  If a checked-out baseline was
       a working baseline, the baseline-controlled collection that
       determined the DAV:baseline-collection for the new baseline MUST
       have been the merge target for that new baseline.
  
  
  14 VERSION-CONTROLLED-COLLECTION FEATURE
  
       As with any versionable resource, when a collection is put under
       version control, a version history resource is created to contain
       versions for that version-controlled collection.  In order to
       preserve standard versioning semantics (a version of a collection
       should not be modifiable), a collection version only records
       information about the version-controlled bindings of that
       collection.
  
       In order to cleanly separate a modification to the namespace from a
       modification to content or dead properties, a version of a
       collection is not itself a collection, but just records in its
       DAV:version-controlled-binding-set property the binding name and
       version history resource of each version-controlled internal member
       of that collection.  If, instead, a collection version contained
       bindings to other versions, creating a new version of a resource
       would require creating a new version of all the collection versions
       that contain that resource, which would cause activities to become
       entangled.  For example, suppose a "feature-12" activity created a
       new version of /x/y/a.html.  If a collection version contained
       bindings to versions of its members, a new version of /x/y would
       have to be created to contain the new version of /x/y/a.html, and a
       new version of /x would have to be created to contain the new
       version of /x/y.  Now suppose a "bugfix-47" activity created a new
       version of /x/z/b.html.  Again, a new version of /x/z and a new
       version of /x would have to be created to contain the new version
       of /x/y/b.html.  But now it is impossible to merge just "bugfix-47"
       into another workspace without "feature-12", because the version of
       /x that contains the desired version of /x/z/b.html also contains
       version of /x/y/a.html created for "feature-12".  If, instead, a
       collection version just records the binding name and version
       history resource of each version-controlled internal member,
       changing the version selected by a member of that collection would
  
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       not require a new version of the collection.  The new version is
       still in the same version history so no new collection version is
       required, and "feature-12" and "bugfix-47" would not become
       entangled.
  
       In the following example, there are three version histories, named
       VH14, VH19, and VH24, where VH14 contains versions of a collection.
       The version-controlled collection /x has version V2 of version
       history VH14 as its DAV:checked-in version.  Since V2 has recorded
       two version controlled bindings, one with binding name "a" to
       version history VH19, and the other with binding name "b" to
       version history VH24, /x MUST have two version-controlled bindings,
       one named "a" to a version-controlled resource for history VH19,
       and the other named "b" to a version-controlled resource for
       history VH24.  The version-controlled resource /x/a currently has
       V4 of VH19 as its DAV:checked-in version, while /x/b has V8 of
       VH24as its DAV:checked-in version.
  
  
                                                           VH19
                                                        +---------+
                                                        | +---+   |
                                                        | |   |V4 |
                                                        | +---+   |
                                                        |   |     |
                                                        |   |     |
                                                        | +---+   |
                                                        | |   |V5 |
                                             VH14       | +---+   |
                                         +---------+    |   |     |
                                         | +---+   |    |   |     |
                a  +---+                 | |   |V1 |    | +---+   |
              ---->|   |checked-in=V4    | +---+   | a  | |   |V6 |
             /     +---+                 |   |   ------>| +---+   |
            /                            |   |  /  |    +---------+
       +---+                             | +---+   |
    /x |   |checked-in=V2                | |   |V2 |
       +---+                             | +---+   |       VH24
            \                            |   |  \  | b  +---------+
             \  b  +---+                 |   |   ------>| +---+   |
              ---->|   |checked-in=V8    | +---+   |    | |   |V7 |
                   +---+                 | |   |V3 |    | +---+   |
                                         | +---+   |    |   |     |
                                         +---------+    |   |     |
                                                        | +---+   |
                                                        | |   |V8 |
                                                        | +---+   |
                                                        |   |     |
                                                        |   |     |
                                                        | +---+   |
                                                        | |   |V9 |
                                                        | +---+   |
                                                        +---------+
  
  
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       For any request (e.g. DELETE, MOVE, COPY) that modifies a version-
       controlled binding of a checked-in version-controlled collection,
       the request MUST fail unless the version-controlled collection has
       a DAV:auto-checkout property.  If the version-controlled collection
       has a DAV:auto-checkout property, standard auto-versioning
       semantics apply.  This functionality allows a versioning unaware
       client to add a version to the collection version history.
  
       Although a collection version only records the version-controlled
       bindings of a collection, a version-controlled collection MAY
       contain both version-controlled and non-version-controlled
       bindings.  Non-version-controlled bindings are not under version
       control, and therefore can be added or deleted without checking out
       the version-controlled collection.  This feature is essential for
       the support of lock null resources, since a lock null resource is a
       temporary internal member of a collection that should only exist
       for the duration of the lock, and should not be captured in the
       version history of that collection.
  
       Note that a collection version captures only a defined subset of
       the state of a collection.  In particular, a version of a
       collection captures its dead properties and its bindings to
       version-controlled resources, but not its live properties or
       bindings to non-version-controlled resources.
  
  
  14.1Version-Controlled Collection Properties
  
       A version-controlled collection has all the properties of a
       collection and of a version-controlled resource.  In addition, the
       version-controlled-collection feature introduces the following
       REQUIRED property for a version-controlled collection.
  
  
  14.1.1    DAV:eclipsed-set (computed)
  
       This property identifies the non-version-controlled internal
       members of the collection that currently are eclipsing a version-
       controlled internal member of the collection.
  
       <!ELEMENT eclipsed-set (href*)>
  
       An UPDATE or MERGE request can give a version-controlled collection
       a version-controlled internal member that has the same name as an
       existing non-version-controlled internal member.  In this case, the
       non-version-controlled internal member takes precedence and is said
       to "eclipse" the new versioned-controlled internal member.  If the
       non-version-controlled internal member is removed (e.g. by a DELETE
       or MOVE), the version-controlled internal member is exposed.
  
  
  
  
  
  
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  14.2Collection Version Properties
  
       A collection has all the properties of a version.  In addition, the
       version-controlled-collection feature introduces the following
       REQUIRED property for a collection version.
  
  
  14.2.1    DAV:version-controlled-binding-set (protected)
  
       This property captures the name and version-history of each
       version-controlled internal member of a collection.
  
       <!ELEMENT version-controlled-binding-set (version-controlled-
       binding*)>
       <!ELEMENT version-controlled-binding (binding-name, version-
       history)>
       <!ELEMENT binding-name (#PCDATA)>
       PCDATA value: URL segment
       <!ELEMENT version-history (href)>
  
  14.3Working Collection Properties
  
       When a server supports the working-resource feature, a client can
       check out a collection version to create a "working collection".
       Unlike a version-controlled collection, which contains bindings to
       version-controlled resources and non-version-controlled resources,
       a working collection contains bindings to version history resources
       and non-version-controlled resources.  In particular, a working
       resource is initialized to contain bindings to the version history
       resources specified by the DAV:version-controlled-binding-set of
       the checked out version.  The members of a working collection can
       then be deleted or moved to another working collection.  Non-
       version-controlled resources can be added to a working collection
       with methods such as PUT, COPY, and MKCOL.  When a working
       collection is checked in, a VERSION-CONTROL request is
       automatically applied to every non-version-controlled member of the
       working collection, and each non-version-controlled member is
       replaced by its newly created version history.  The DAV:version-
       controlled-binding-set of the new version resulting from checking
       in a working collection contains the binding name and version
       history URL for each member of the working collection.
  
  
  14.3.1    DAV:version-controlled-binding-set
  
       This property determines the DAV:version-controlled-binding-set
       property of the collection version that results from checking in
       this working collection (see Section 14.2.1).
  
  
  14.4Additional OPTIONS Semantics
  
       If the server supports the version-controlled-collection feature,
       it MUST include "version-controlled-collection" as a field in the
  
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       DAV response header from an OPTIONS request on any resource that
       supports any versioning properties, reports, or methods.
  
  
  14.5Additional DELETE Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-modify-checked-in-parent): If the request-URL
       identifies a version-controlled resource, the DELETE MUST fail when
       the collection containing the version-controlled resource is a
       checked-in version-controlled collection, unless DAV:auto-checkout
       semantics will automatically check out the version-controlled
       collection.
  
  
  14.6Additional MKCOL Semantics
  
     Additional Preconditions:
  
       If the request creates a new resource that is automatically placed
       under version control, all preconditions for VERSION-CONTROL apply
       to the request.
  
     Additional Postconditions:
  
       If the new collection is automatically put under version control,
       all postconditions for VERSION-CONTROL apply to the request.
  
  
  14.7Additional COPY Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-copy-collection-version): If the source of the request
       is a collection version, the request MUST fail..
  
  
  14.8Additional MOVE Semantics
  
     Additional Preconditions:
  
       (DAV:cannot-modify-checked-in-parent): If the source of the request
       is a version-controlled resource, the request MUST fail when the
       collection containing the source is a checked-in version-controlled
       collection, unless DAV:auto-checkout semantics will automatically
       check out that version-controlled collection.
  
       (DAV:cannot-modify-destination-checked-in-parent): If the source of
       the request is a version-controlled resource, the request MUST fail
       when the collection containing the destination is a checked-in
       version-controlled collection, unless DAV:auto-checkout semantics
       will automatically check out that version-controlled collection.
  
  
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  14.9Additional VERSION-CONTROL Semantics
  
     Additional Preconditions:
  
        (DAV:cannot-modify-checked-in-parent): If the parent of the
       request-URL is a checked-in version-controlled collection, the
       request MUST fail unless DAV:auto-checkout semantics will
       automatically check out that version-controlled collection.
  
  
  14.10     Additional CHECKOUT Semantics
  
     Additional Postconditions:
  
       (DAV:initialize-version-history-bindings): If the request has been
       applied to a collection version, the new working collection MUST be
       initialized to contain a binding to each of the history resources
       identified in the DAV:version-controlled-binding-set of that
       collection version.
  
  
  14.11     Additional CHECKIN Semantics
  
     Additional Postconditions:
  
       (DAV:initialize-version-controlled-bindings): If the request-URL
       identified a version-controlled collection, then the DAV:version-
       controlled-binding-set of the new collection version MUST contain a
       DAV:version-controlled-binding that identifies the binding name and
       version history for each version-controlled binding of the version-
       controlled collection.
  
       (DAV:version-control-working-collection-members): If the request-
       URL identified a working collection, a VERSION-CONTROL request MUST
       have been automatically applied to every non-version-controlled
       member of the working collection, and each non-version-controlled
       members MUST have been replaced by its newly created version
       history.  If a working collection member was a non-version-
       controlled collection, every member of the non-version-controlled
       collection MUST have been placed under version control before the
       non-version-controlled collection was placed under version control.
       The DAV:version-controlled-binding-set of the new collection
       version MUST contain a DAV:version-controlled-binding that
       identifies the binding name and the version history URL for each
       member of the working collection.
  
  
  14.12     Additional UPDATE and MERGE Semantics
  
     Additional Postconditions:
  
       (DAV:update-version-controlled-collection-members): If the request
       modified the DAV:checked-in version of a version-controlled
  
  
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       collection, then the version-controlled members of that version-
       controlled collection MUST have been updated.  In particular:
       - A version-controlled internal member MUST have been deleted if
       its version history is not identified by the DAV:version-
       controlled-binding-set of the new DAV:checked-in version.
       - A version-controlled internal member for a given version history
       MUST have been renamed if its binding name differs from the
       DAV:binding-name for that version history in the DAV:version-
       controlled-binding-set of the new DAV:checked-in version.
       - A new version-controlled internal member MUST have been created
       when a version history is identified by the DAV:version-controlled-
       binding-set of the DAV:checked-in version, but there was no member
       of the version-controlled collection for that version history.
       If a new version-controlled member is in a workspace that already
       has a version-controlled resource for that version history, then
       the new version-controlled member MUST be just a binding (i.e.
       another name for) that existing version-controlled resource.
       Otherwise, the content and dead properties of the new version-
       controlled member MUST have been initialized to be those of the
       version specified for that version history by the request.  If no
       version is specified for that version history by the request, the
       root version of that version history MUST have been used.
  
  
  15 OPTIONAL REPORTS
  
  
  15.1DAV:expand-property REPORT
  
       Many properties consist of a set of one or more DAV:href elements.
       The DAV:expand-property REPORT provides a mechanism for retrieving
       in one request the properties from the resources identified by
       those DAV:href elements.  This report not only decreases the number
       of requests required, but also allows the server to minimize the
       number of separate read transactions required on the underlying
       versioning store.
  
     Marshalling:
  
       The request body MUST be a DAV:expand-property XML element.
  
       <!ELEMENT expand-property (property*)>
       <!ELEMENT property (property*)>
       <!ATTLIST property name NMTOKEN #REQUIRED>
       name value: a property element type
       <!ATTLIST property namespace NMTOKEN "DAV:">
       namespace value: an XML namespace
  
       The request MAY include a Depth header.
  
       The response body for a successful request MUST be a
       DAV:multistatus XML element.
  
       multistatus: see RFC 2518, Section 12.9
  
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       The properties reported in the DAV:prop elements of the
       DAV:multistatus element MUST be those identified by the
       DAV:property elements in the DAV:expand-property element.  If there
       are DAV:property elements nested within a DAV:property element,
       then every DAV:href in the value of the corresponding property is
       replaced by a DAV:response element whose DAV:prop elements report
       the values of the properties identified by the nested DAV:property
       elements.  The nested DAV:property elements can in turn contain
       DAV:property elements, so that multiple levels of DAV:href
       expansion can be requested.
  
       Note that a validating parser MUST be aware that the DAV:expand-
       property report effectively modifies the DTD of every property by
       replacing every occurrence of "href" in the DTD with "href |
       response".
  
  
  15.1.1    Example - DAV:expand-property
  
       This example describes how to query a version-controlled resource
       to determine the DAV:creator-display-name and DAV:activity-set of
       every version in the version history of that version-controlled
       resource.
  
       >>REQUEST
  
         REPORT /foo.html HTTP/1.1
         Host: www.webdav.org
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:expand-property xmlns:D="DAV:">
           <D:property name="version-history">
             <D:property name="version-set">
               <D:property name="creator-displayname"/>
               <D:property name="activity-set"/>
             </D:property>
           </D:property>
         </D:expand-property>
  
       >>RESPONSE
  
         HTTP/1.1 207 Multi-Status
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
  
         <?xml version="1.0" encoding="utf-8" ?>
         <D:multistatus xmlns:D="DAV:">
           <D:response>
             <D:href>http://www.webdav.org/foo.html</D:href>
             <D:propstat>
               <D:prop>
  
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                 <D:version-history>
                   <D:response>
                     <D:href>http://repo.webdav.org/his/23</D:href>
                     <D:propstat>
                       <D:prop>
                         <D:version-set>
                           <D:response>
  
       <D:href>http://repo.webdav.org/his/23/ver/1<D:href>
                             <D:propstat>
                               <D:prop>
                                 <D:creator-displayname>Fred</D:creator-
       displayname>
                                 <D:activity-set> <D:href>
                                   http://www.webdav.org/ws/dev/sally
                                 </D:href> </D:activity-set> </D:prop>
                               <D:status>HTTP/1.1 200 OK</D:status>
                             </D:propstat> </D:response>
                           <D:response>
  
       <D:href>http://repo.webdav.org/his/23/ver/2<D:href>
                             <D:propstat>
                               <D:prop>
                                 <D:creator-displayname>Sally</D:creator-
       displayname>
                                 <D:activity-set> <D:href>
                                   http://repo.webdav.org/act/add-refresh-
       cmd
                                 </D:href> </D:activity-set> </D:prop>
                               <D:status>HTTP/1.1 200 OK</D:status>
                             </D:propstat> </D:response>
                         </D:version-set> </D:prop>
                       <D:status>HTTP/1.1 200 OK</D:status>
                     </D:propstat> </D:response>
                 </D:version-history> </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat> </D:response>
         </D:multistatus>
  
       In this example, the DAV:creator-displayname and DAV:activity-set
       properties of the versions in the DAV:version-set of the
       DAV:version-history of http://www.webdav.org/foo.html are reported.
  
  
  16 INTERNATIONALIZATION CONSIDERATIONS
  
       This specification has been designed to be compliant with the IETF
       Policy on Character Sets and Languages [RFC2277].  Specifically,
       where human-readable strings exist in the protocol, either their
       charset is explicitly stated, or XML mechanisms are used to specify
       the charset used.  Additionally, these human-readable strings all
       have the ability to express the natural language of the string.
  
  
  
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       Most of the human-readable strings in this protocol appear in
       properties, such as DAV:creator-displayname.  As defined by RFC
       2518, properties have their values marshaled as XML.  XML has
       explicit provisions for character set tagging and encoding, and
       requires that XML processors read XML elements encoded, at minimum,
       using the UTF-8 [RFC2279] encoding of the ISO 10646 multilingual
       plane.  The charset parameter of the Content-Type header, together
       with the XML "encoding" attribute, provide charset identification
       information for MIME and XML processors.  Proper use of the charset
       header with XML is described in RFC 3023.  XML also provides a
       language tagging capability for specifying the language of the
       contents of a particular XML element.  XML uses either IANA
       registered language tags (see RFC 1766) or ISO 639 language tags in
       the "xml:lang" attribute of an XML element to identify the language
       of its content and attributes.
  
       DeltaV applications, since they build upon WebDAV, are subject to
       the internationalization requirements specified in RFC 2518,
       Section 16.  In brief, these requirements mandate the use of XML
       character set tagging, character set encoding, and language tagging
       capabilities.  Additionally, they strongly recommend reading RFC
       3023 for instruction on the use of MIME media types for XML
       transport and the use of the charset header.
  
       Within this specification, a label is a human-readable string that
       is marshaled in the Label header and as XML in request entity
       bodies.  When used in the Label header, the value of the label is
       encoded using UTF-8.
  
  
  17 SECURITY CONSIDERATIONS
  
       All of the security considerations of WebDAV discussed in RFC 2518,
       Section 17 also apply to WebDAV versioning.  Some aspects of the
       versioning protocol help address security risks introduced by
       WebDAV, but other aspects can increase these security risks.  These
       issues are detailed below.
  
  
  17.1Auditing and Traceability
  
       WebDAV increases the ease with which a remote client can modify
       resources on a web site, but this also increases the risk of
       important information being overwritten and lost, either through
       user error or user maliciousness.  The use of WebDAV versioning can
       help address this problem by guaranteeing that previous information
       is saved in the form of immutable versions, and therefore is easily
       available for retrieval or restoration.  In addition, the version
       history provides a log of when changes were made, and by whom.
       When requests are appropriately authenticated, the history
       mechanism provides a clear audit trail for changes to web
       resources.  This can often significantly improve the ability to
       identify the source of the security problem, and thereby help guard
       against it in the future.
  
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  17.2Increased Need for Access Control
  
       WebDAV versioning provides a variety of links between related
       pieces of information.  This can increase the risk that
       authentication or authorization errors allow a client to locate
       sensitive information. For example, if version history is not
       appropriately protected by access control, a client can use the
       version history of a public resource to identify later versions of
       that resource that the author intended to keep private.  This
       increases the need for reliable authentication and accurate
       authorization.
  
       A WebDAV versioning client should be designed to handle a mixture
       of 200 (OK) and 404 (Forbidden) responses on attempts to access the
       properties and reports that are supported by a resource.   For
       example, a particular user may be authorized to access the content
       and dead properties of a version-controlled resource, but not be
       authorized to access the DAV:checked-in, DAV:checked-out, or
       DAV:version-history properties of that resource.
  
  
  17.3Security Through Obscurity
  
       While it is acknowledged that "obscurity" is not an effective means
       of security, it is often a good technique to keep honest people
       honest.  Within this protocol, version URLs, version history URLs,
       and working resource URLs are generated by the server and can be
       properly obfuscated so as not to draw attention to them.  For
       example, a version of "http://foobar.com/reviews/salaries.html"
       might be assigned a URL such as "http://foobar.com/repo/4934943".
  
  
  17.4Denial of Service
  
       The auto-versioning mechanism provided by WebDAV can result in a
       large number of resources being created on the server, since each
       update to a resource could potentially result in the creation of a
       new version resource.  This increases the risk of a denial of
       service attack that exhausts the storage capability of a server.
       This risk is especially significant because it can be an
       unintentional result of something like an aggressive auto-save
       feature provided by an editing client.  A server can decrease this
       risk by using delta storage techniques to minimize the cost of
       additional versions, and by limiting auto-versioning to a locking
       client, and thereby decreasing the number of inadvertent version
       creations.
  
  
  18 IANA CONSIDERATIONS
  
       This document uses the namespace defined by RFC 2518 for XML
       elements.  All other IANA considerations from RFC 2518 are also
       applicable to WebDAV Versioning.
  
  
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  19 INTELLECTUAL PROPERTY
  
       The following notice is copied from RFC 2026, Section 10.4, and
       describes the position of the IETF concerning intellectual property
       claims made against this document.
  
       The IETF takes no position regarding the validity or scope of any
       intellectual property or other rights that might be claimed to
       pertain to the implementation or use other technology described in
       this document or the extent to which any license under such rights
       might or might not be available; neither does it represent that it
       has made any effort to identify any such rights.  Information on
       the procedures of the IETF with respect to rights in standards-
       track and standards-related documentation can be found in BCP-11.
       Copies of claims of rights made available for publication and any
       assurances of licenses to be made available, or the result of an
       attempt made to obtain a general license or permission for the use
       of such proprietary rights by implementers or users of this
       specification can be obtained from the IETF Secretariat.
  
  
       The IETF invites any interested party to bring to its attention any
       copyrights, patents or patent applications, or other proprietary
       rights that may cover technology that may be required to practice
       this standard.  Please address the information to the IETF
       Executive Director.
  
  
  20 ACKNOWLEDGEMENTS
  
       This protocol is the collaborative product of the authors and the
       rest of the DeltaV design team: Boris Bokowski (OTI), Bruce Cragun
       (Novell), Jim Doubek (Macromedia), David Durand (INSO), Lisa
       Dusseault (Xythos), Tim Ellison (OTI), Chuck Fay (FileNet), Yaron
       Goland, Mark Hale (Interwoven), Henry Harbury (Merant), James Hunt,
       Jeff McAffer (OTI), Juergen Reuter, Edgar Schwarz (Marconi), Eric
       Sedlar (Oracle), Bradley Sergeant, Greg Stein, and John Vasta
       (Rational).  We would like to acknowledge the foundation laid for
       us by the authors of the WebDAV and HTTP protocols upon which this
       protocol is layered, and the invaluable feedback from the WebDAV
       and DeltaV working groups.
  
  
  21 REFERENCES
  
       [ISO639] ISO, "Code for the representation of names of languages",
       ISO 639:1988, 1998.
  
       [RFC1766] H.T.Alvestrand, "Tags for the Identification of
       Languages", Uninett, 1995.
  
       [RFC2026] S.Bradner, "The Internet Standards Process", Harvard,
       1996.
  
  
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       [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
       Requirement Levels", Harvard, 1997.
  
       [RFC2277] H.T.Alvestrand, "IETF Policy on Character Sets and
       Languages", BCP 18, Uninett, 1998.
  
       [RFC2279] F.Yergeau, "UTF-8, a transformation format of ISO 10646",
       Alis Technologies, 1998.
  
       [RFC2396] T.Berners-Lee, R.Fielding, L.Masinter, "Uniform Resource
       Identifiers (URI): Generic Syntax", MIT, U.C.Irvine, Xerox, 1998.
  
       [RFC2518] Y.Goland, E.Whitehead, A.Faizi, S.R.Carter, D.Jensen,
       "HTTP Extensions for Distributed Authoring - WEBDAV", Microsoft,
       U.C.Irvine, Netscape, Novell, 1999.
  
       [RFC2616] R.Fielding, J.Gettys, J.C.Mogul, H.Frystyk, L.Masinter,
       P.Leach, and T.Berners-Lee, "Hypertext Transfer Protocol --
       HTTP/1.1", U.C.Irvine, Compaq, Xerox, Microsoft, MIT/LCS, 1999.
  
       [RFC3023]M.Murata, S.St.Laurent, D.Kohn, "XML Media Types", IBM,
       simonstl.com, Skymoon Ventures, 2001.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  22 AUTHORS' ADDRESSES
  
       Geoffrey Clemm
       Rational Software
       20 Maguire Road, Lexington, MA 02421
       Email: geoffrey.clemm@rational.com
  
       Jim Amsden
       IBM
       3039 Cornwallis, Research Triangle Park, NC 27709
       Email: jamsden@us.ibm.com
  
       Christopher Kaler
       Microsoft
       One Microsoft Way, Redmond, WA 90852
       Email: ckaler@microsoft.com
  
       Jim Whitehead
       UC Santa Cruz, Dept. of Computer Science
       1156 High Street, Santa Cruz, CA 95064
       Email: ejw@cse.ucsc.edu
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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