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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 4791

Network Working Group                                           C. Daboo
Internet-Draft                                                    ISAMET
Expires: January 18, 2006                                B. Desruisseaux
                                                                  Oracle
                                                            L. Dusseault
                                                                    OSAF
                                                           July 17, 2005


               Calendaring Extensions to WebDAV (CalDAV)
                       draft-dusseault-caldav-07

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on January 18, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies a set of methods, headers, message bodies,
   properties, and reports that define calendar access extensions to the
   WebDAV protocol.  The new protocol elements are intended to make
   WebDAV-based calendaring and scheduling an interoperable standard
   that supports single-user calendar access, calendar management,



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   calendar sharing, and calendar publishing.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1   Notational Conventions . . . . . . . . . . . . . . . . . .  5
     1.2   XML Namespaces . . . . . . . . . . . . . . . . . . . . . .  5
     1.3   Method Preconditions and Postconditions  . . . . . . . . .  6
   2.  CalDAV Requirements Overview . . . . . . . . . . . . . . . . .  7
   3.  Capability Discovery . . . . . . . . . . . . . . . . . . . . .  8
     3.1   CalDAV Server Support  . . . . . . . . . . . . . . . . . .  8
       3.1.1   Example: Using OPTIONS for the Discovery of
               Support for CalDAV . . . . . . . . . . . . . . . . . .  8
   4.  Calendar Resources . . . . . . . . . . . . . . . . . . . . . .  9
     4.1   Calendaring Data Model . . . . . . . . . . . . . . . . . .  9
       4.1.1   Calendar Server  . . . . . . . . . . . . . . . . . . .  9
       4.1.2   Recurrence and the Data Model  . . . . . . . . . . . . 10
     4.2   Calendar Home  . . . . . . . . . . . . . . . . . . . . . . 10
     4.3   Calendar Collection  . . . . . . . . . . . . . . . . . . . 11
     4.4   Calendaring Properties . . . . . . . . . . . . . . . . . . 11
       4.4.1   CALDAV:calendar-description Property . . . . . . . . . 12
       4.4.2   CALDAV:calendar-component-restriction-set Property . . 12
       4.4.3   CALDAV:calendar-restrictions Property  . . . . . . . . 13
     4.5   Calendar Object Resource Restrictions in Calendar
           Collections  . . . . . . . . . . . . . . . . . . . . . . . 14
     4.6   Creating Resources . . . . . . . . . . . . . . . . . . . . 15
       4.6.1   MKCALENDAR Method  . . . . . . . . . . . . . . . . . . 16
         4.6.1.1   Status Codes . . . . . . . . . . . . . . . . . . . 17
         4.6.1.2   Example - MKCALENDAR . . . . . . . . . . . . . . . 17
       4.6.2   Creating Calendar Object Resources . . . . . . . . . . 18
   5.  Calendaring Access Control . . . . . . . . . . . . . . . . . . 20
     5.1   Calendaring Privileges . . . . . . . . . . . . . . . . . . 20
       5.1.1   CALDAV:read-free-busy Privilege  . . . . . . . . . . . 20
       5.1.2   Privilege aggregation and the
               DAV:supported-privilege-set property . . . . . . . . . 20
         5.1.2.1   Partial example of DAV:supported-privilege-set
                   property . . . . . . . . . . . . . . . . . . . . . 21
     5.2   Additional Principal Properties  . . . . . . . . . . . . . 22
       5.2.1   CALDAV:calendar-home-URL Property  . . . . . . . . . . 22
       5.2.2   CALDAV:calendar-address-set Property . . . . . . . . . 22
       5.2.3   Example: Searching calendar home based on a
               calendar address . . . . . . . . . . . . . . . . . . . 23
   6.  Calendaring Reports  . . . . . . . . . . . . . . . . . . . . . 25
     6.1   REPORT Method  . . . . . . . . . . . . . . . . . . . . . . 25
     6.2   Reports on collections containing calendar collections . . 25
     6.3   Reports and recurring items  . . . . . . . . . . . . . . . 25
     6.4   CALDAV:calendar-query Report . . . . . . . . . . . . . . . 26
       6.4.1   Example: Partial retrieval of events by time range . . 27



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       6.4.2   Example: Partial retrieval of recurring events . . . . 31
       6.4.3   Example: Expanded retrieval of recurring events  . . . 31
       6.4.4   Example: Retrieval of to-dos by alarm time range . . . 31
       6.4.5   Example: Retrieval of event by UID . . . . . . . . . . 32
       6.4.6   Example: Retrieval of events by participation
               status . . . . . . . . . . . . . . . . . . . . . . . . 33
       6.4.7   Example: Retrieval of events only  . . . . . . . . . . 34
     6.5   CALDAV:calendar-multiget Report  . . . . . . . . . . . . . 35
       6.5.1   Example: CALDAV:calendar-multiget Report . . . . . . . 36
     6.6   CALDAV:free-busy-query Report  . . . . . . . . . . . . . . 38
       6.6.1   Example: CALDAV:free-busy-query Report . . . . . . . . 40
   7.  Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     7.1   Client-to-client Interoperability  . . . . . . . . . . . . 42
     7.2   Sychronization Operations  . . . . . . . . . . . . . . . . 42
       7.2.1   Use of Reports . . . . . . . . . . . . . . . . . . . . 42
         7.2.1.1   Restrict the Time Range  . . . . . . . . . . . . . 42
         7.2.1.2   Synchronize by Time Range  . . . . . . . . . . . . 42
         7.2.1.3   Synchronization Process  . . . . . . . . . . . . . 43
       7.2.2   Restrict the Properties Returned . . . . . . . . . . . 45
     7.3   Use of Locking . . . . . . . . . . . . . . . . . . . . . . 46
     7.4   Finding calendars  . . . . . . . . . . . . . . . . . . . . 46
   8.  XML Element Definitions  . . . . . . . . . . . . . . . . . . . 48
     8.1   CALDAV:calendar-query XML Element  . . . . . . . . . . . . 48
     8.2   CALDAV:calendar-data-only XML Element  . . . . . . . . . . 48
     8.3   CALDAV:calendar-data XML Element . . . . . . . . . . . . . 48
       8.3.1   CALDAV:comp XML Element  . . . . . . . . . . . . . . . 49
       8.3.2   CALDAV:allcomp XML Element . . . . . . . . . . . . . . 49
       8.3.3   CALDAV:allprop XML Element . . . . . . . . . . . . . . 50
       8.3.4   CALDAV:prop XML Element  . . . . . . . . . . . . . . . 50
       8.3.5   CALDAV:expand-recurrence-set XML Element . . . . . . . 51
       8.3.6   CALDAV:limit-recurrence-set XML Element  . . . . . . . 51
     8.4   CALDAV:filter XML Element  . . . . . . . . . . . . . . . . 52
       8.4.1   CALDAV:comp-filter XML Element . . . . . . . . . . . . 52
       8.4.2   CALDAV:prop-filter XML Element . . . . . . . . . . . . 53
       8.4.3   CALDAV:param-filter XML Element  . . . . . . . . . . . 53
       8.4.4   CALDAV:is-defined XML Element  . . . . . . . . . . . . 54
       8.4.5   CALDAV:text-match XML Element  . . . . . . . . . . . . 54
     8.5   CALDAV:time-range XML Element  . . . . . . . . . . . . . . 55
     8.6   DAV:response XML Element . . . . . . . . . . . . . . . . . 56
     8.7   CALDAV:calendar-multiget XML Element . . . . . . . . . . . 56
     8.8   CALDAV:free-busy-query XML Element . . . . . . . . . . . . 57
   9.  Internationalization Considerations  . . . . . . . . . . . . . 58
   10.   Security Considerations  . . . . . . . . . . . . . . . . . . 59
   11.   IANA Consideration . . . . . . . . . . . . . . . . . . . . . 60
     11.1  Namespace Registration . . . . . . . . . . . . . . . . . . 60
   12.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 61
   13.   References . . . . . . . . . . . . . . . . . . . . . . . . . 62
     13.1  Normative References . . . . . . . . . . . . . . . . . . . 62



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     13.2  Informative References . . . . . . . . . . . . . . . . . . 62
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 63
   A.  CalDAV Method Privilege Table (Normative)  . . . . . . . . . . 64
   B.  Changes  . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
     B.1   Changes in -07 . . . . . . . . . . . . . . . . . . . . . . 65
     B.2   Changes in -06 . . . . . . . . . . . . . . . . . . . . . . 65
     B.3   Changes in -05 . . . . . . . . . . . . . . . . . . . . . . 66
     B.4   Changes in -04 . . . . . . . . . . . . . . . . . . . . . . 67
     B.5   Changes in -03 . . . . . . . . . . . . . . . . . . . . . . 67
     B.6   Changes in -02 . . . . . . . . . . . . . . . . . . . . . . 67
     B.7   Changes in -01 . . . . . . . . . . . . . . . . . . . . . . 67
       Intellectual Property and Copyright Statements . . . . . . . . 69







































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1.  Introduction

   The concept of using HTTP [5] and WebDAV [4] as a basis for a
   calendaring server is by no means a new concept: it was discussed in
   the IETF CALSCH working group as early as 1997 or 1998.  Several
   companies have implemented calendaring servers using HTTP PUT/GET to
   upload and download iCalendar [3] objects, and using WebDAV PROPFIND
   to get listings of resources.  However, those implementations do not
   interoperate because there are many small and big decisions to be
   made in how to model calendaring data as WebDAV resources, as well as
   how to implement required features that aren't already part of
   WebDAV.  This document proposes a standard way of modeling calendar
   data in WebDAV, with additional features to make calendar access work
   well.

   Discussion of this Internet-Draft is taking place on the mailing list
   <http://lists.osafoundation.org/mailman/listinfo/ietf-caldav>.

1.1  Notational Conventions

   The augmented BNF used by this document to describe protocol elements
   is described in Section 2.1 of [5].  Because this augmented BNF uses
   the basic production rules provided in Section 2.2 of [5], those
   rules apply to this document as well.

   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 [1].

   The term "protected" is used in the Conformance field of property
   definitions as defined in Section 1.4.2 of RFC3253 [7].

   When XML element types in the namespaces "DAV:" and
   "urn:ietf:params:xml:ns:caldav" are referenced in this document
   outside of the context of an XML fragment, the string "DAV:" and
   "CALDAV:" will be prefixed to the element type names respectively.

1.2  XML Namespaces

   Definitions of XML elements in this document use XML element type
   declarations (as found in XML Document Type Declarations), described
   in Section 3.2 of [10].

   The namespace "urn:ietf:params:xml:ns:caldav" is reserved for the XML
   elements defined in this specification, its revisions, and related
   CalDAV specifications.  It MUST NOT be used for proprietary
   extensions.




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   Note that the XML declarations used in this document are incomplete,
   in that they do not include namespace information.  Thus, the reader
   MUST NOT use these declarations as the only way to create valid
   CalDAV properties or to validate CalDAV XML element type.  Some of
   the declarations refer to XML elements defined by WebDAV which use
   the "DAV:" namespace.  Wherever such elements appear, they are
   explicitly given the "DAV:" prefix to help avoid confusion.

   Also note that some CalDAV XML element names are identical to WebDAV
   XML element names, though their namespace differs.  Care MUST be
   taken not to confuse the two sets of names.

1.3  Method Preconditions and Postconditions

   A "precondition" of a method describes the state of the server that
   must be true for that method to be performed.  A "postcondition" of a
   method describes the state of the server that must be true after that
   method has been completed.  If a method precondition or postcondition
   for a request is not satisfied, the response status of the request
   MUST be either 403 (Forbidden) if the request should not be repeated
   because it will always fail, or 409 (Conflict) if it is expected that
   the user might be able to resolve the conflict and resubmit the
   request.

   In order to allow better client handling of 403 and 409 responses, a
   distinct XML element type is associated with each method precondition
   and postcondition of a request.  When a particular precondition is
   not satisfied or a particular postcondition cannot be achieved, 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, the DAV:error
   element would appear in the appropriate DAV:responsedescription
   element.


















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2.  CalDAV Requirements Overview

   This section lists what functionality is required of a CalDAV server.
   To advertise support for CalDAV, a server:

   o  MUST support WebDAV Class 1 [4].

   o  MUST support WebDAV ACL [9] with the privilege defined in
      Section 5.1 of this document.

   o  MUST support transport over TLS [2] as defined in RFC2818 [6].

   o  MUST support strong ETags to support disconnected operations.

   o  MUST support all required calendaring REPORTs defined in this
      document.

   o  MUST advertise calendaring REPORTs via the DAV:supported-report-
      set property as defined in Versioning Extensions to WebDAV [7].

   In addition, a server:

   o  SHOULD support the MKCALENDAR method defined in Section 4.6.1 of
      this document.



























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3.  Capability Discovery

3.1  CalDAV Server Support

   If a server supports the CalDAV features described in this document,
   it MUST include "calendar-access" as a field in the DAV response
   header from an OPTIONS request on any resource that supports any
   calendar properties, reports, methods, or privilege.  A value of
   "calendar-access" in the DAV header MUST indicate that the server
   supports all MUST level requirements and REQUIRED features specified
   in this document.

3.1.1  Example: Using OPTIONS for the Discovery of Support for CalDAV

   >> Request <<


   OPTIONS /home/bernard/ HTTP/1.1
   Host: cal.example.com

   >> Response <<


   HTTP/1.1 200 OK
   Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
   Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT
   Allow: MKCALENDAR, ACL
   DAV: 1, 2, access-control, calendar-access
   Content-Length: 0

   In this example, the OPTIONS response indicates that the server
   supports CalDAV on this collection, therefore the "/home/bernard/"
   collection may be used as a parent for calendar collections as the
   MKCALENDAR method is available, and as a possible target for REPORT
   requests for calendaring reports.
















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4.  Calendar Resources

4.1  Calendaring Data Model

   One of the features which has made WebDAV a successful protocol is
   its firm data model.  This makes it a useful framework for other
   applications such as calendaring.  This specification follows the
   same pattern by developing all features based on a well-described
   data model.

   In the CalDAV data model, every VEVENT, VTODO, VJOURNAL, and
   VFREEBUSY component is contained in an individual resource, referred
   to as a "calendar object resource".  Each calendar object resource
   may be individually locked and have individual WebDAV properties.
   These resources are placed into WebDAV collections with a mostly-
   fixed structure.

4.1.1  Calendar Server

   A CalDAV server is a calendaring-aware engine combined with a WebDAV
   repository.  A WebDAV repository is a set of WebDAV collections,
   containing other WebDAV resources, within a unified URL namespace.
   For example, the repository "http://www.example.com/webdav/" may
   contain WebDAV collections and resources, all of which have URLs
   beginning with "http://www.example.com/webdav/".  Note that the root
   URL "http://www.example.com/" may not itself be a WebDAV repository
   (for example, if the WebDAV support is implemented through a servlet
   or other Web server extension).

   A WebDAV repository MAY include calendar data in some parts of its
   URL namespace, and non-calendaring data in other parts.

   A WebDAV repository can advertise itself as a CalDAV server if it
   supports the functionality defined in this specification at any point
   within the root of the repository.  That might mean that calendaring
   data is spread throughout the repository and mixed with non-calendar
   data in nearby collections (e.g., calendar data may be found in
   /home/lisa/calendar/ as well as in /home/bernard/calendar/, and non-
   calendar data in /home/lisa/contacts/).  Or, it might mean that
   calendar data can be found only in certain sections of the repository
   (e.g., /caldav/).  Calendaring features are only required in the
   repository sections that are or contain calendaring objects.  So a
   repository confining calendar data to the /caldav/ collection would
   only need to support the CalDAV required features within that
   collection.

   The CalDAV server or repository is the canonical location for
   calendar data and state information.  Both CalDAV servers and clients



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   MUST ensure that the data is consistent and compliant.  Clients may
   submit requests to change data or download data.  Clients may store
   calendar objects offline and attempt to synchronize at a later time.
   However, clients MUST be prepared for calendar data on the server to
   change between the time of last synchronization and when attempting
   an update, as calendar collections may be shared and accessible via
   multiple clients.  HTTP ETags and other features help this work.

4.1.2  Recurrence and the Data Model

   Recurrence is an important part of the data model because it governs
   how many resources are expected to exist.  This specification models
   a recurring calendar component and its recurrence exceptions as a
   single resource.  In this model, recurrence patterns, recurrence
   dates, exception dates, and exception information are all part of the
   data in a single calendar object resource.  This model avoids
   problems of limiting how many recurrence instances to store in the
   repository, how to keep instances in synch with the recurring
   calendar component, and how to link recurrence exceptions with the
   recurring calendar component.  It also results in less data to
   synchronize between client and server, and makes it easier to make
   changes to all recurrence instances or to a recurrence pattern.  It
   makes it easier to create a recurring calendar component, and easier
   to delete all recurrence instances.

   Clients are not forced to retrieve information about all recurrence
   instances of a recurring component.  The CALDAV:calendar-query and
   CALDAV:calendar-multiget REPORTs defined in this document allow
   clients to retrieve only recurrence instances that overlap a given
   time range.

4.2  Calendar Home

   Calendar home collections are manifested to clients as a WebDAV
   resource collection, identified by a URL.  A calendar home collection
   MUST report the DAV:collection and CALDAV:calendar-home XML elements
   in the value of the DAV:resourcetype property.  The element type
   declaration for CALDAV:calendar-home is:

       <!ELEMENT calendar-home EMPTY>

   Typically, calendar users will group all the calendar collections
   that they own under a common calendar home collection.  Grouping a
   user's calendar collections under a common calendar home collection
   allow one to obtain free-busy time information for all this user's
   calendar with a single CALDAV:free-busy-query REPORT request
   targetted at the calendar home collection.




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   Creation of calendar home collections is viewed as an administrative
   task and is not covered by this specification.

   Calendar home collections MUST NOT contain other calendar home
   collections.  Multiple calendar home collections MAY be children of
   the same WebDAV collection.

   A calendar home collection MAY contain additional collections and
   non-collection resources of types not defined here.  How such items
   are used is not defined by this specification.  However, additional
   collections contained in a calendar home collection MUST NOT contain
   calendar home collections.

4.3  Calendar Collection

   Calendar collections are manifested to clients as a WebDAV resource
   collection, identified by a URL.  A calendar collection MUST report
   the DAV:collection and CALDAV:calendar XML elements in the value of
   the DAV:resourcetype property.  The element type declaration for
   CALDAV:calendar is:

       <!ELEMENT calendar EMPTY>

   A calendar collection contains resources that represent the iCalendar
   objects within a calendar.  A calendar collection may be created
   through provisioning (e.g., automatically created when a user's
   account is created), or it may be created through MKCALENDAR (see
   Section 4.6.1).  This can be useful for a user to create a second
   calendar (e.g., soccer schedule) or for users to share a calendar
   (e.g., team events or conference room).  Note however that this
   document doesn't define what extra calendar collections are for,
   users must rely on non-standard cues to find out what a calendar
   collection is for, or use the CALDAV:calendar-description property
   defined in Section 4.4.1 to provide such a cue.

   Calendar collections MUST NOT contain other calendar collections.
   Multiple calendar collections MAY be children of the same WebDAV
   collection.

   A calendar collection MAY contain additional collections and non-
   collection resources of types not defined here.  How such items are
   used is not defined by this specification.  However, additional
   collections contained in a calendar collection MUST NOT contain
   calendar collections.

4.4  Calendaring Properties

   This section defines properties that may be defined on calendar home



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   collections and/or calendar collections.

4.4.1  CALDAV:calendar-description Property

   Name: calendar-description

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Provides a human-readable description of what this calendar
      home or calendar collection represents.

   Conformance: This property MAY be protected and SHOULD NOT be
      returned by a PROPFIND allprop request (as defined in Section
      12.14.1 of [4]).  Servers MUST indicate the human language of the
      description using the xml:lang attribute and SHOULD consider the
      HTTP Accept-Language request header when selecting one of multiple
      available languages.

   Description: The CALDAV:calendar-description property MAY be defined
      on any calendar home or calendar collection.  If present, the
      property contains a description of the calendar home or calendar
      collection that is suitable for presentation to a user.

   Definition:

      <!ELEMENT calendar-description (#PCDATA) >

   Example:

      <C:calendar-description xml:lang="fr-CA"
         xmlns:C="urn:ietf:params:xml:ns:caldav"
      >Calendrier de Bernard Desruisseaux</C:calendar-description>


4.4.2  CALDAV:calendar-component-restriction-set Property

   Name: calendar-component-restriction-set

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies the type of calendar component types (e.g.,
      VEVENT, VTODO, etc.) that calendar object resources may contain in
      a calendar collection.

   Conformance: This property MAY be protected and SHOULD NOT be
      returned by a PROPFIND allprop request (as defined in Section
      12.14.1 of [4]).




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   Description: The CALDAV:calendar-component-restriction-set property
      MAY be defined on any calendar collection to specify the calendar
      component types that the CalDAV server support in the calendar
      object resources contained in the calendar collection.  CalDAV
      servers MAY allow users to set this property on any calendar
      collection by using PROPPATCH to allow them to restrict the
      calendar component types themselves.  The element <C:comp
      name="VTIMEZONE"> MUST only be specified if support for calendar
      object resources that only contains VTIMEZONE components is
      provided or desired.  Support for VTIMEZONE components in calendar
      object resources that contain VEVENT or VTODO components is always
      assumed.

   Definition:

       <!ELEMENT calendar-component-restriction-set (comp*)>

   Example:


       <C:calendar-component-restriction-set
           xmlns:C="urn:ietf:params:xml:ns:caldav">
         <C:comp name="VEVENT"/>
         <C:comp name="VTODO"/>
       </C:calendar-component-restriction-set>


   [[Comment.1: CalDAV servers that will allow users to modify this
   property will require a way to advertise what they are capable of
   supporting.  Perhap they could return a calendar-component-
   restriction-set element as part of the value of the calendar-
   restrictions property. --desruisseaux]]

4.4.3  CALDAV:calendar-restrictions Property

   Name: calendar-restrictions

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies restrictions on a calendar collection.

   Conformance: This property MAY be protected and SHOULD NOT be
      returned by a PROPFIND allprop request (as defined in Section
      12.14.1 of [4]).







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   Description: The CALDAV:calendar-restrictions property MAY be defined
      on any calendar collection to specify restrictions a CalDAV server
      may have on a calendar collection.

   Definition:


       <!ELEMENT calendar-restrictions (calendar-data-only?,
                                        calendar-data?)>


   Example:


       <C:calendar-restrictions xmlns:C="urn:ietf:params:xml:ns:caldav">
         <C:calendar-data-only/>
         <C:calendar-data content-type="text/calendar" version="2.0"/>
       </C:calendar-restrictions>



4.5  Calendar Object Resource Restrictions in Calendar Collections

   Calendar object resources contained in calendar collections MUST NOT
   contain more than one type of calendar component (e.g., VEVENT,
   VTODO, etc.) with the exception of VTIMEZONE components which MUST be
   specified for each unique TZID parameter value specified in the
   iCalendar object.  For instance, a calendar object resource can
   contain two VEVENT components and one VTIMEZONE component, but it
   cannot contain one VEVENT component and one VTODO component.

   The UID property value of the calendar components contained in a
   calendar object resource MUST be unique in the scope of the calendar
   collection, and all its descendant collections, in which the calendar
   object resource is contained.

   Calendar components in a calendar collection that have different UID
   property values MUST be stored in separate calendar object resources.

   Calendar components with the same UID property value, in a given
   calendar collection, MUST be contained in the same calendar object
   resource.  This ensures that all components in a recurrence "set" are
   contained in the same calendar object resource.  In that case there
   will be one component without a RECURRENCE-ID property (the component
   that defines the recurrence pattern) and all the rest will have that
   property (these are the recurrence exceptions).

   For example, given the following iCalendar object:



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   BEGIN:VCALENDAR
   CALSCALE:GREGORIAN
   PRODID:-//Example, Inc.\, Inc.//Example App//EN
   VERSION:2.0
   BEGIN:VEVENT
   UID:1@example.com
   SUMMARY:One-off Meeting
   DTSTAMP:20041210T183904Z
   DTSTART:20041207T120000Z
   DTEND:20041207T130000Z
   END:VEVENT
   BEGIN:VEVENT
   UID:2@example.com
   SUMMARY:Weekly Meeting
   DTSTAMP:20041210T183838Z
   DTSTART:20041206T120000Z
   DTEND:20041206T130000Z
   RRULE:FREQ=WEEKLY
   END:VEVENT
   BEGIN:VEVENT
   UID:2@example.com
   RECURRENCE-ID:20041213T120000Z
   DTSTAMP:20041210T183838Z
   DTSTART:20041213T130000Z
   END:VEVENT
   END:VCALENDAR

   The VEVENT component with the UID value "1@example.com", would be
   stored in its own calendar object resource.  The two VEVENT
   components with the UID value "2@example.com", which represent a
   recurring event where one recurrence instance has been overridden,
   would be stored in the same calendar object resource.

4.6  Creating Resources

   The creation of calendar collections and calendar object resources
   may be initiated by either a CalDAV client or by the CalDAV server.
   For example, a server might come preconfigured with a user's calendar
   collection, or the CalDAV client might request the server to create a
   new calendar collection for a given user.  Servers might populate
   events as calendar objects inside a calendar collection, or clients
   might request the server to create events.  Either way, both client
   and server MUST comply with the requirements in this document, and
   MUST understand objects appearing in calendar collections or
   according to the data model defined here.






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4.6.1  MKCALENDAR Method

   An HTTP request using the MKCALENDAR method creates a new calendar
   collection resource.  A server MAY restrict calendar collection
   creation to particular collections.

   Support for MKCALENDAR on the server is OPTIONAL because some
   calendar stores only support one calendar per user (or principal) and
   those are typically pre-created for each account.  However, servers
   and clients are strongly encouraged to support MKCALENDAR whenever
   possible to allow users to create multiple calendar collections to
   better help organize their data.

   Clients SHOULD use the DAV:displayname property for a human-readable
   name of the calendar.  This requires the clients to issue a PROPPATCH
   request to change the DAV:displayname property to the appropriate
   value immediately after issuing the MKCALENDAR request.  Clients
   SHOULD NOT set the DAV:displayname property to be the same as any
   other calendar collection at the same URI "level".  When displaying
   calendar collections to users, clients SHOULD check the DAV:
   displayname property and use that value as the name of the calendar.
   In the event that the DAV:displayname property is empty, the client
   MAY use the last part of the calendar collection URI as the name.

   If a MKCALENDAR request fails, the server state preceding the request
   MUST be restored.

   Marshalling:

      If a request body is included, it MUST be a CALDAV:mkcalendar XML
      element.


   <!ELEMENT mkcalendar ANY>

      If a response body for a successful request is included, it MUST
      be a CALDAV:mkcalendar-response XML element.


   <!ELEMENT mkcalendar-response 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-URI.




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      (CALDAV:calendar-collection-location-bad): The Request-URI MUST
      identify a location where a calendar collection can be created.

      (CALDAV:insufficient-privilege): The DAV:bind privilege MUST be
      granted to the current user.

   Postconditions:

      (CALDAV:initialize-calendar-collection): A new calendar collection
      exists at the Request-URI.  The DAV:resourcetype of the calendar
      collection MUST contain both DAV:collection and CALDAV:calendar
      XML elements.


4.6.1.1  Status Codes

   201 (Created) - The calendar collection resource was created in its
   entirety.

   403 (Forbidden) - This indicates at least one of two conditions: 1)
   the server does not allow the creation of calendar collections at the
   given location in its namespace, or 2) the parent collection of the
   Request-URI exists but cannot accept members.

   405 (Method Not Allowed) - MKCALENDAR can only be executed on a null
   resource.

   409 (Conflict) - A collection cannot be made at the Request-URI until
   one or more intermediate collections have been created.

   415 (Unsupported Media Type)- The server does not support the request
   type of the body.

   507 (Insufficient Storage) - The resource does not have sufficient
   space to record the state of the resource after the execution of this
   method.

4.6.1.2  Example - MKCALENDAR

   >> Request <<


   MKCALENDAR /home/lisa/calendar/ HTTP/1.1
   Host: cal.example.com
   Content-Length: 0






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   >> Response <<


   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Content-Length: 0

   In this example, a new calendar collection is created at
   http://cal.example.com/home/lisa/calendar/.

4.6.2  Creating Calendar Object Resources

   Clients typically populate calendar collections with calendar object
   resources.  The URL for each calendar object resource is entirely
   arbitrary, and does not need to bear a specific relationship (but
   might) to the calendar object resource's subject, scheduled time, UID
   or other metadata.  A new calendar object resource must have a unique
   URL, otherwise the new component would instead be an update to an
   existing calendar object resource.

   When servers create new resources, it's not hard for the server to
   choose a unique URL.  It's slightly tougher for clients, because a
   client might not want to examine all resources in the collection, and
   might not want to lock the entire collection to ensure that a new one
   isn't created with a name collision.  However, there are http
   features to mitigate this.  If the client intends to create a new
   non-collection resource, such as a new VEVENT, the client SHOULD use
   the HTTP header "If-None-Match: *" on the PUT request.  The Request-
   URI on the PUT request MUST include the target collection, where the
   resource is to be created, plus the name of the resource in the last
   path segment.  The last path segment could be a random number, or it
   could be a sequence number, or a string related to the object's
   SUMMARY property.  No matter how the name is chosen, the "If-None-
   Match" header ensures that the client cannot overwrite an existing
   resource even if it has accidentally chosen a duplicate resource
   name.

   Servers SHOULD return an ETag header containing the actual ETag of
   the newly created resource on a successful creation.












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   >> Request <<


   PUT /lisa/calendar/newevent.ics HTTP/1.1
   If-None-Match: *
   Host: cal.example.com
   Content-Type: text/calendar
   Content-Length: xxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:20010712T182145Z-123401@example.com
   DTSTART:20010714T170000Z
   DTEND:20010715T040000Z
   SUMMARY:Bastille Day Party
   END:VEVENT
   END:VCALENDAR

   >> Response <<


   HTTP/1.1 201 Created
   Content-Length: 0
   ETag: "123456789-000-111"

   The request to change an existing event is the same, but with a
   specific ETag in the "If-Match" header, rather than the "If-None-
   Match" header.

   As indicated in Section 3.10 of RFC 2445 [3], the URL of calendar
   object resources containing (an arbitrary set of) calendaring and
   scheduling information may be suffixed by ".ics", and the URL of
   calendar object resources containing free or busy time information
   may be suffixed by ".ifb".

   Preconditions for PUT within calendar collections:

      (CALDAV:uid-already-exists): The component UID chosen is not
      unique and the client must choose another if it attempts again.

      (CALDAV:invalid-calendar-resource): The iCalendar object syntax or
      structure was invalid.  (Note that the server MAY support upload
      formats other than iCalendar but then the server MUST validate
      each component uploaded according to the chosen format syntax.)





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5.  Calendaring Access Control

5.1  Calendaring Privileges

   A CalDAV server MUST support WebDAV  ACL [9].  WebDAV ACL provides a
   framework for an extensible list of privileges on WebDAV collections
   and ordinary resources.  A CalDAV server MUST also support the
   calendaring privilege defined in this section.

5.1.1  CALDAV:read-free-busy Privilege

   Calendar users often wish to allow other users to see their busy time
   information, without viewing the other details of the calendar
   components (location, summary, attendees).  This allows a significant
   amount of privacy while still allowing those other users to schedule
   meetings at times when the calendar user is likely to be free.

   The CALDAV:read-free-busy privilege controls which calendar
   collections and calendar object resources are examined when a free-
   busy-query REPORT is run (see Section 6.6).  This privilege can be
   granted on calendar collections or calendar object resources.
   Servers MUST support this privilege on calendar collections and any
   calendar object resources within those collections.


     <!ELEMENT read-free-busy EMPTY>

   The CALDAV:read-free-busy privilege is aggregated in the DAV:read
   privilege.  Note that if an ACL grants the privilege CALDAV:read-
   free-busy, the client may not expect to be granted access to GET,
   HEAD, OPTIONS and PROPFIND.

5.1.2  Privilege aggregation and the DAV:supported-privilege-set
       property

   In the WebDAV ACL standard, servers MUST support the DAV:supported-
   privilege-set property to show which privileges are abstract, which
   privileges are supported, how the privileges relate to another, and
   to provide text descriptions (particularly useful for custom
   privileges).  The relationships between privileges involves showing
   which privilege is a subset or a superset of another privilege.  For
   example, because reading the ACL property is considered a more
   specific privilege than the DAV:read privilege (a subset of the total
   set of actions are allowed), it may be aggregated under the DAV:read
   privilege.  Although the list of supported privileges MAY vary
   somewhat from server to server (the WebDAV ACL specification leaves
   room for a fair amount of diversity in server implementations), the
   following restriction MUST hold for a CalDAV server:



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   o  The server MUST support the CALDAV:read-free-busy privilege.  The
      CALDAV:read-free-busy privilege MUST be non-abstract, and MUST be
      aggregated under the DAV:read privilege.


5.1.2.1  Partial example of DAV:supported-privilege-set property

   This is a partial example of how the DAV:supported-privilege-set
   property could look on a server supporting CalDAV.  Note that
   aggregation is shown in the structure of the DAV:supported-privilege
   elements containing each other.

   <D:supported-privilege-set xmlns:D="DAV:"
         xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:supported-privilege>
       <D:privilege><D:all/></D:privilege>
       <D:abstract/>
       <D:description xml:lang="en"
   >Any operation</D:description>
       <D:supported-privilege>
         <D:privilege><D:read/></D:privilege>
         <D:description xml:lang="en"
   >Read any object</D:description>
         <D:supported-privilege>
           <D:privilege><D:read-acl/></D:privilege>
           <D:description xml:lang="en"
   >Read ACL</D:description>
         </D:supported-privilege>
         <D:supported-privilege>
           <D:privilege><D:read-current-user-privilege-set/>
           </D:privilege>
           <D:description xml:lang="en"
   >Read current user privilege set</D:description>
         </D:supported-privilege>
         <D:supported-privilege>
           <D:privilege>
             <C:read-free-busy/>
           </D:privilege>
           <D:description xml:lang="en"
   >Read busy time information</D:description>
         </D:supported-privilege>
       </D:supported-privilege>
       <D:supported-privilege>
         <D:privilege><D:write/></D:privilege>
         <D:description xml:lang="en"
   >Write any object</D:description>
       ...
     </D:supported-privilege>



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   </D:supported-privilege-set>


5.2  Additional Principal Properties

   This section defines additional properties for WebDAV principal
   resources as defined in RFC3744 [9].

5.2.1  CALDAV:calendar-home-URL Property

   Name: calendar-home-URL

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Identify the URL of any calendar home collections owned by
      the associated principal resource.

   Conformance: This property MAY be protected and SHOULD NOT be
      returned by a PROPFIND allprop request (as defined in Section
      12.14.1 of [4]).  Support for this property is RECOMMENDED.

   Description:

   Definition:

       <!ELEMENT calendar-home-URL (DAV:href*) >

   Example:

       <C:calendar-home-URL xmlns:D="DAV:"
                            xmlns:C="urn:ietf:params:xml:ns:caldav">
         <D:href>http://cal.example.com/home/bernard/</D:href>
       </C:calendar-home-URL>


5.2.2  CALDAV:calendar-address-set Property

   Name: calendar-address-set

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Identify the calendar addresses of the associated principal
      resource.

   Conformance: This property MAY be protected and SHOULD NOT be
      returned by a PROPFIND allprop request (as defined in Section
      12.14.1 of [4]).  Support for this property is RECOMMENDED.  This
      property SHOULD be searchable using the DAV:principal-property-



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      search REPORT.  The DAV:principal-search-property-set REPORT
      SHOULD identify this property as such.

   Description: This property is mostly meant to discover the calendar
      home collection URLs of the principal associated with a given
      calendar address by using the DAV:principal-property-search
      REPORT.

   Definition:

       <!ELEMENT calendar-address-set (DAV:href*) >

   Example:

       <C:calendar-address-set xmlns:D="DAV:"
                               xmlns:C="urn:ietf:params:xml:ns:caldav">
         <D:href>mailto:bernard@example.com</D:href>
         <D:href>mailto:bernard.desruisseaux@example.com</D:href>
       </C:calendar-address-set>


5.2.3  Example: Searching calendar home based on a calendar address

   In this example, the client request the CALDAV:calendar-home-URL of
   the principal resources whose CALDAV:calendar-address-set property
   contains the substring "mailto:bernard@example.com".  In addition,
   the client request the DAV:displayname to be returned with the
   matching principals.

   The response shows that only one principal resource meet the search
   specification, "Bernard Desruisseaux".




















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   >> Request <<


   REPORT /users/ HTTP/1.1
   Host: cal.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Depth: 0

   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-property-search xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:property-search>
       <D:prop>
         <C:calendar-address-set/>
       </D:prop>
       <D:match>mailto:bernard@example.com</D:match>
     </D:property-search>
     <D:prop>
       <C:calendar-home-URL/>
       <D:displayname/>
     </D:prop>
   </D:principal-property-search>


   >> 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:"
                  xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:response>
       <D:href>http://cal.example.com/users/bernard</D:href>
       <D:propstat>
         <D:prop>
           <C:calendar-home-URL>
             <D:href>http://cal.example.com/home/bernard/</D:href>
           </C:calendar-home-URL>
           <D:displayname>Bernard Desruisseaux</D:displayname>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>



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6.  Calendaring Reports

   This section defines the reports which a CalDAV server MUST support
   on calendar collections and calendar object resources.

   CalDAV servers MUST advertise support for those reports with the DAV:
   supported-report-set property defined in RFC3253 [7].

   Some of these reports allow calendar data (from possibly multiple
   resources) to be returned.  Clients SHOULD request the DAV:getetag
   property whenever executing reports that return calendar data, to
   ensure that any local cache used for synchronization is kept up to
   date with the latest changes on the server

6.1  REPORT Method

   The REPORT method (defined in Section 3.6 of RFC3253 [7]) provides an
   extensible mechanism for obtaining information about a resource.
   Unlike the PROPFIND method, which returns the value of one or more
   named properties, the REPORT method can involve more complex
   processing.  REPORT is valuable in cases where the server has access
   to all of the information needed to perform the complex request (such
   as a query), and where it would require multiple requests for the
   client to retrieve the information needed to perform the same
   request.

   A server that supports calendar-access MUST support the DAV:expand-
   property report (defined in Section 3.8 of RFC3253 [7]).

6.2  Reports on collections containing calendar collections

   A WebDAV collection which contains one or more calendar collections
   is not a new type of resource, but it may support these new REPORT.
   If so, then the REPORT is expected to have the semantics of including
   information from all the calendar data contained in the collection,
   and its children, recursively.  These collections may contain more
   than only calendar related resources.  It's up to the server, if it
   supports this REPORT on a normal WebDAV collection, to find calendar
   object resources and decide what to do with non-calendar resources
   and whether those may also appear in the collection or its children.

   If these reports are supported on ordinary collections the server
   advertises the capability with the DAV:supported-report-set property
   as already described.

6.3  Reports and recurring items

   Some of the reports defined in CalDAV can be targetted at calendar



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   object resources within a specific time range.  To determine whether
   a calendar object resource matches the time range filter element, the
   start and end times for the particular type of object are determined
   and then compared to the requested time range.  If the start and end
   overlap the requested time range, then the calendar object resource
   matches the filter element.  The rules defined in [3] for determining
   the actual start and end times of calendar components MUST be used.

   When such time range filtering is used, special consideration must be
   given to recurring calendar components such as VEVENT and VTODO
   components.  The server MUST expand recurring items to determine.
   whether any one or more recurrence instances overlap the requested
   time range.  If any one instance overlaps the time range, then the
   calendar object resource matches the filter element.

   In addition, CalDAV provides three ways to determine which recurrence
   instances are returned from the recurrence set.  The three options
   are:

   1.  Return all the calendar components contained in the calendar
       object resources.  This includes the recurrence instance that
       defines the recurrence pattern, referred to as the "master
       instance", as well as the recurrence instances that define
       exceptions to the recurrence pattern, referred to as the
       "overriden instances".  Because of the rules defined in
       Section 4.1.2 all recurrence instances of a recurring component
       will always be in the same calendar object resource.

   2.  Return the "master" instance and only the "overridden instances"
       that overlap the specified time range.  This avoids the need for
       clients to process recurrence instances outside of the time range
       they are interested in.

   3.  Return an "expanded" set of calendar components that represent
       only those instances in the recurrence set that overlap the
       specified time range.  This avoids the need for clients to do any
       recurrence processing themselves as the server does the expansion
       for them and provides the list of instances.


6.4  CALDAV:calendar-query Report

   The CALDAV:calendar-query REPORT performs a search for all calendar
   object resources that match a specified search filter.  The response
   of this report will contain all the WebDAV properties and calendar
   object resource data specified in the request.  In the case of the
   CALDAV:calendar-data XML element, one can explicitly specify the
   calendar components and properties that should be returned in the



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   calendar object resource data that matches the search filter.

   The format of this report is modeled on the PROPFIND method.  The
   request and response bodies of the CALDAV:calendar-query report use
   XML elements that are also used by PROPFIND.  In particular the
   request can include XML elements to request WebDAV properties to be
   returned.  When that occurs the response should follow the same
   behavior as PROPFIND with respect to the DAV:multistatus response
   elements used to return specific property results.  For instance, a
   request to retrieve the value of a property which does not exist is
   an error and MUST be noted with a response XML element which contains
   a 404 (Not Found) status value.

   Support for the calendar-query REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CALDAV:calendar-query XML element as
      defined in Section 8.1.

      The response body for a successful request MUST be a DAV:
      multistatus XML element (i.e., the response uses the same format
      as the response for PROPFIND).  In the case where there are no
      response elements, the returned multistatus XML element is empty.

      The response body for a successful calendar-query REPORT request
      MUST contain a DAV:response element for each iCalendar object that
      matched the search filter.  The declaration of the DAV:response
      element from Section 12.9.1 of RFC2518 [4] has been modified to
      allow the CALDAV:calendar-data element within the DAV:response
      element, see Section 8.6

   Preconditions:

      None.

   Postconditions:

      (DAV:number-of-matches-within-limits): The number of matching
      calendar object resources must fall within server-specific,
      predefined limits.  For example, this condition might be triggered
      if a search specification would cause the return of an extremely
      large number of responses.


6.4.1  Example: Partial retrieval of events by time range

   In this example, the client requests the server to return specific



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   components and properties of the VEVENT components that overlap the
   time range from September 2nd, 2004 at 00:00:00 am UTC to September
   2nd, 2004 at 11:59:59 pm UTC.  In addition the DAV:getetag property
   is also requested and returned as part of the response.  Note that
   the third calendar object returned is a recurring event whose first
   instance lies outside of the requested time range, but whose second
   instance does overlap the time range.












































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   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <D:getetag/>
     </D:prop>
     <C:calendar-data>
       <C:comp name="VCALENDAR">
         <C:allprop/>
         <C:comp name="VEVENT">
           <C:prop name="X-ABC-GUID"/>
           <C:prop name="UID"/>
           <C:prop name="DTSTART"/>
           <C:prop name="DTEND"/>
           <C:prop name="DURATION"/>
           <C:prop name="EXDATE"/>
           <C:prop name="EXRULE"/>
           <C:prop name="RDATE"/>
           <C:prop name="RRULE"/>
           <C:prop name="LOCATION"/>
           <C:prop name="SUMMARY"/>
         </C:comp>
         <C:comp name="VTIMEZONE">
           <C:allprop/>
           <C:allcomp/>
         </C:comp>
       </C:comp>
     </C:calendar-data>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:time-range start="20040902T000000Z"
                         end="20040903T000000Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<




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   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:"
                  xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:response>
       <D:href
   >http://cal.example.com/home/bernard/calendar/ev102.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   DTSTART:20040902T100000Z
   DTEND:20040902T120000Z
   SUMMARY:Design meeting
   UID:34222-232@example.com
   X-ABC-GUID:E1CX4zp-0005Ld-21@example.com
   END:VEVENT
   END:VCALENDAR
       </C:calendar-data>
     </D:response>
     <D:response>
       <D:href
   >http://cal.example.com/home/bernard/calendar/mtg103.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"ff11fb-23ba4d"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   DTSTART:20040902T130000Z
   DTEND:20040902T150000Z
   SUMMARY:Design meeting - Part II
   UID:63409-868@example.com
   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT



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   END:VCALENDAR
       </C:calendar-data>
     </D:response>
     <D:response>
       <D:href
   >http://cal.example.com/home/bernard/calendar/mtg104.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"7834cd-63fd2c"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   DTSTART:20040901T130000Z
   DTEND:20040901T150000Z
   RRULE:FREQ=DAILY;COUNT=2
   SUMMARY:Design meeting - Part III
   UID:63409-451@example.com
   X-ABC-GUID:E1CX5Dr-0008ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
       </C:calendar-data>
     </D:response>
   </D:multistatus>


6.4.2  Example: Partial retrieval of recurring events

   Todo: Example with CALDAV:limit-recurrence-set.

6.4.3  Example: Expanded retrieval of recurring events

   Todo: Example with CALDAV:expand-recurrence-set.

6.4.4  Example: Retrieval of to-dos by alarm time range

   In this example, the client requests the server to return the VTODO
   components that have an alarm trigger scheduled in the specified time
   range.









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   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
     </D:prop>
     <C:calendar-data/>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VTODO">
           <C:comp-filter name="VALARM">
             <C:time-range start="20041121T000000Z"
                           end="20041122T000000Z"/>
           </C:comp-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


6.4.5  Example: Retrieval of event by UID

   In this example, the client requests the server to return the VEVENT
   component that has the UID property set to
   "20041121-FEEBDAED@foo.org".



















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   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
     </D:prop>
     <C:calendar-data/>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:prop-filter name="UID">
             <C:text-match
                caseless="no">20041121-FEEBDAED@foo.org</C:text-match>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


6.4.6  Example: Retrieval of events by participation status

   In this example, the client requests the server to return the VEVENT
   components that have the ATTENDEE property with the value
   "mailto:bernard@example.com" and for which the PARTSTAT parameter is
   set to "NEEDS-ACTION".


















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   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
     </D:prop>
     <C:calendar-data/>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:prop-filter name="ATTENDEE"/>
             <C:text-match
               caseless="yes">mailto:bernard@example.com</C:text-match>
             <C:param-filter name="PARTSTAT"/>
               <C:text-match caseless="no">NEEDS-ACTION</C:text-match>
             </C:param-filter>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


6.4.7  Example: Retrieval of events only

   In this example, the client requests the server to return all VEVENT
   components.

















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   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
     </D:prop>
     <C:calendar-data/>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:is-defined/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


6.5  CALDAV:calendar-multiget Report

   The CALDAV:calendar-multiget REPORT is used to retrieve specific
   calendar object resources from within a collection, if the Request-
   URI is a collection, or to retrieve a specific calendar object
   resource, if the Request-URI is a calendar object resource.  This
   report is similar to the CALDAV:calendar-query REPORT (see
   Section 6.4), except that it takes a list of DAV:href elements
   instead of a CALDAV:filter element to determine which calendar object
   resources to return.

   Support for the calendar-multiget REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CALDAV:calendar-multiget XML element
      (see Section 8.7, which MUST contain at least one DAV:href XML
      element, and one optional CALDAV:calendar-data element as defined
      in Section 8.3.  If the Request-URI is a collection resource, then
      the DAV:href elements MUST refer to resources within that
      collection, and they MAY refer to resources at any depth within
      the collection.  As a result the "Depth" header MUST be ignored by
      the server and SHOULD NOT be sent by the client.  If the Request-
      URI refers to a non-collection resource, then there MUST be a



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      single DAV:href element that is equal to the Request-URI.

      The response body for a successful request MUST be a DAV:
      multistatus XML element.  In the case where there are no response
      elements, the returned multistatus XML element is empty.

      The response body for a successful CALDAV:calendar-multiget REPORT
      request MUST contain a DAV:response element for each calendar
      object resource referenced by the provided set of DAV:href
      elements.  The DAV:response element is as defined in Section 8.6.

      In the case of an error accessing any of the provided DAV:href
      resources, the server MUST return the appropriate error status
      code in the DAV:status element of the corresponding DAV:response
      element.

   Preconditions:

      None.

   Postconditions:

      None.


6.5.1  Example: CALDAV:calendar-multiget Report

   In this example, the client requests the server to return specific
   properties of the VEVENT components references by specific URIs.  In
   addition the DAV:getetag property is also requested and returned as
   part of the response.  Note that in this example, the resource at
   http://cal.example.com/home/bernard/calendar/mtg1.ics does not exist,
   resulting in an error status response.


















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   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-multiget xmlns:D="DAV:"
                        xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <D:getetag/>
     </D:prop>
     <C:calendar-data>
       <C:comp name="VCALENDAR">
         <C:allprop/>
         <C:comp name="VEVENT">
           <C:prop name="UID"/>
           <C:prop name="DTSTART"/>
           <C:prop name="DTEND"/>
           <C:prop name="DURATION"/>
           <C:prop name="EXDATE"/>
           <C:prop name="EXRULE"/>
           <C:prop name="RDATE"/>
           <C:prop name="RRULE"/>
           <C:prop name="LOCATION"/>
           <C:prop name="SUMMARY"/>
         </C:comp>
         <C:comp name="VTIMEZONE">
           <C:allprop/>
           <C:allcomp/>
         </C:comp>
       </C:comp>
     </C:calendar-data>
     <D:href
   >http://cal.example.com/home/bernard/calendar/ev102.ics</D:href>
     <D:href
   >http://cal.example.com/home/bernard/calendar/mtg1.ics</D:href>
   </C:calendar-multiget>












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   >> 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:"
                  xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:response>
       <D:href
   >http://cal.example.com/home/bernard/calendar/ev102.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   DTSTART:20040902T100000Z
   DTEND:20040902T120000Z
   SUMMARY:Design meeting
   UID:34222-232@example.com
   END:VEVENT
   END:VCALENDAR
       </C:calendar-data>
     </D:response>
     <D:response>
       <D:href
   >http://cal.example.com/home/bernard/calendar/mtg1.ics</D:href>
       <D:status>HTTP/1.1 404 Resource not found</D:status>
     </D:response>
   </D:multistatus>


6.6  CALDAV:free-busy-query Report

   The CALDAV:free-busy-query REPORT generates a VFREEBUSY component
   containing free busy information for all relevant calendar components
   within calendar collections which have the CALDAV:read-free-busy or
   DAV:read privilege granted for the current user.

   Only VEVENT components, without a TRANSP property or with the TRANSP
   property set to a value other than "TRANSPARENT", and VFREEBUSY
   components are used to generate the free busy time information.



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   Support for the CALDAV:free-busy-query REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CALDAV:free-busy-query XML element (see
      Section 8.8, which MUST contain at least one CALDAV:time-range XML
      element, as defined in Section 8.5.

      The response body for a successful request MUST be a DAV:
      multistatus XML element.  In the case where there are no response
      elements, the returned multistatus XML element is empty.

      The response body for a successful CALDAV:free-busy-query REPORT
      request MUST contains a DAV:response element for each calendar
      collection for which free-busy information has been computed.
      Each DAV:response element contains a single CALDAV:calendar-data
      XML element as defined in Section 8.3.  The CALDAV:calendar-data
      XML element MUST contain an iCalendar object with a single
      VFREEBUSY component, with zero or more FREEBUSY property values
      that describe the busy time intervals for the calendar object
      resources being targeted, and with other properties set according
      to the rules of iCalendar.  This report only returns busy time
      information.  Applications desiring free time information MUST
      infer this from available busy time information.

   When the Request-URI for a CALDAV:free-busy-query REPORT is a
   calendar collection, the free-busy data is implicitly determined from
   the calendar object resources containing VEVENT and VFREEBUSY
   components within the calendar collection, irrespective of the value
   of any Depth header included in the REPORT request.  Only calendar
   object resources containing VEVENT or VFREEBUSY components that have
   the CALDAV:read-free-busy privilege granted to the current user will
   be computed in the response.

   When the Request-URI for a CALDAV:free-busy-query REPORT is a non-
   calendar collection, the scope of the report is governed by the value
   of the Depth header in the request as follows:

      Depth: 0 - an empty VFREEBUSY component will be returned as there
      is no valid calendar data to be scanned on the collection.

      Depth: 1 - free-busy data for any calendar collections immediately
      within the target collection is returned.

      Depth: infinity - free-busy data for all calendar collections
      within any sub-collections of the target collection is returned.

   Note that as per the requirements of Section 6.3 the server MUST



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   expand any recurring items to determine whether any instances
   contribute to the free busy information in the requested time range.

   Preconditions:

      None.

   Postconditions:

      (DAV:number-of-matches-within-limits): The number of matching
      calendar object resources must fall within server-specific,
      predefined limits.  For example, this condition might be triggered
      if a search specification would cause the return of an extremely
      large number of responses.


6.6.1  Example: CALDAV:free-busy-query Report

   In this example, the client requests the server to return free-busy
   information on the calendar collection /home/bernard/calendar/,
   between 9:00 AM and 5:00 PM on 2nd September 2004.  The server
   responds indicating three busy time intervals of one hour, two hours
   and 30 minutes during the course of the time interval being examined.

   >> Request <<

   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:free-busy-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <C:time-range start="20040902T090000Z"
                     end="20040902T170000Z"/>
   </C:free-busy-query>














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   >> 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:"
                  xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:response>
       <D:href>http://cal.example.com/home/bernard/calendar/</D:href>
       <D:status>HTTP/1.1 200 OK</D:status>
       <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VFREEBUSY
   DTSTAMP:20050125T090000Z
   DTSTART:20040902T090000Z
   DTEND:20040902T170000Z
   FREEBUSY:20040902T090000Z/PT1H,
    20040902T120000Z/PT2H,
    20040902T160000Z/PT30M
   END:VFREEBUSY
   END:VCALENDAR
   </C:calendar-data>
     </D:response>
   </D:multistatus>
























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7.  Guidelines

7.1  Client-to-client Interoperability

   There are a number of actions clients can take which will be legal
   (the server will not return errors) but which can degrade
   interoperability with other client implementations accessing the same
   data.  For example, a recurrence rule could be replaced with a set of
   recurrence dates, a single recurring event could be replaced with a
   set of independent resources to represent each recurrence, or the
   start/end time values can be translated from the original timezone to
   another timezone.  Although these are iCalendar interoperability best
   practices and not limited only to CalDAV usage, interoperability
   problems are likely to be more evident in CalDAV use cases.

7.2  Sychronization Operations

   WebDAV already provides functionality required to synchronize a
   collection or set of collections, make changes offline, and a simple
   way to resolve conflicts when reconnected.  Strong ETags are the key
   to making this work, but these are not required of all WebDAV
   servers.  Since offline functionality is more important to Calendar
   applications than to other WebDAV applications, CalDAV servers MUST
   support strong ETags.

7.2.1  Use of Reports

7.2.1.1  Restrict the Time Range

   The reports provided in CalDAV can be used by clients to optimize
   their performance in terms of network bandwidth usage, and resource
   consumption on the local client machine.  Both of those issues are
   certainly major considerations for mobile or handheld devices with
   limited capacity, but they are also relevant to desktop client
   applications in cases where the calendar collections contain large
   amounts of data.

   Typically clients present calendar data to users in views that span a
   finite time interval, so whenever possible clients should only
   retrieve calendar items from the server using CALDAV:calendar-query
   report combined with a time-range element to limit the scope of
   returned items to just those needed to populate the current view.

7.2.1.2  Synchronize by Time Range

   Typically in a calendar, historical data (events, to-dos etc. that
   have completed prior to the current date) do not change, though they
   may be deleted.  As a result, a client can speed up the



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   synchronization process by only considering data for the present time
   and the future up to a reasonable limit (e.g., one week, one month).
   If the user then tries to examine a portion of the calendar outside
   of the range that has been synchronized, the client can perform
   another synchronization operation on the new time interval being
   examined.  This "just-in-time" synchronization can minimize bandwidth
   for common user interaction behaviors.

7.2.1.3  Synchronization Process

   If a client wants to support calendar data synchronization, as
   opposed to downloading calendar data each time it is needed, it needs
   to cache the component resources URI and ETag along with the actual
   calendar data.  Whilst the URI remains static for the lifetime of the
   component, the ETag will change with each successive change to the
   component data.  Thus to synchronize a local data cache with the
   server, the client can first fetch the URI/ETag pairs for the time
   interval being considered, and compare those results with the cached
   data.  Any cached component whose ETag differs from that on the
   server needs to be synchronized.

   In order to properly detect the changes between the server and client
   data, the client will need to keep a record of which items have been
   created, changed or deleted since the last synchronization operation
   so that it can reconcile those changes with the data on the server.

   An example of how to do that would be the following:



      The client issues a CALDAV:calendar-query REPORT request for a
      specific time range, and asks for only the DAV:getetag property to
      be returned:


















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   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:caldav">
    <D:prop>
      <D:getetag/>
    </D:prop>
    <C:filter>
      <C:comp-filter name="VCALENDAR">
        <C:comp-filter name="VEVENT">
          <C:time-range start="20040902T000000Z"
                        end="20040903T000000Z"/>
        </C:comp-filter>
      </C:comp-filter>
    </C:filter>
   </C:calendar-query>

      The client then uses the results to determine which components
      have changed, been created or deleted on the server and how those
      relate to locally cached components that may have changed, been
      created or deleted.  If the client determines that there are items
      on the server that need to be fetched, the client issues a CALDAV:
      calendar-multiget report to fetch the actual data:























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   REPORT /home/bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-multiget xmlns:D="DAV:"
                        xmlns:C="urn:ietf:params:xml:ns:caldav">
    <D:prop>
      <D:getetag/>
    </D:prop>
    <C:calendar-data>
      <C:comp name="VCALENDAR">
      <C:allprop/>
      <C:comp name="VEVENT">
        <C:prop name="UID"/>
        <C:prop name="DTSTART"/>
        <C:prop name="DTEND"/>
        <C:prop name="DURATION"/>
        <C:prop name="EXDATE"/>
        <C:prop name="EXRULE"/>
        <C:prop name="RDATE"/>
        <C:prop name="RRULE"/>
        <C:prop name="LOCATION"/>
        <C:prop name="SUMMARY"/>
      </C:comp>
      <C:comp name="VTIMEZONE">
        <C:allprop/>
        <C:allcomp/>
      </C:comp>
      </C:comp>
    </C:calendar-data>
    <D:href
   >http://cal.example.com/home/bernard/calendar/evt1.ics</D:href>
    <D:href
   >http://cal.example.com/home/bernard/calendar/mtg1.ics</D:href>
   </C:calendar-multiget>


7.2.2  Restrict the Properties Returned

   Clients may not need all the properties in a calendar component when
   presenting information to the user.  Since some property data can be
   large (e.g., ATTACH or ATTENDEE lists) clients can choose to ignore
   those by only requesting the specific items it knows it will use,
   through use of the CALDAV:calendar-data XML element in the relevant
   reports.



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   However, if a client needs to make a change to a component, it can
   only change the entire component data via a PUT request.  There is no
   way to incrementally make a change to a set of properties within a
   calendar component resource.  As a result the client will have to
   cache the entire set of properties on a resource that is being
   changed.

7.3  Use of Locking

   WebDAV locks can be used to prevent two clients modifying the same
   resource from either overwriting each others' changes (though that
   problem can also be solved by using ETags) and also to prevent the
   user from making changes that will conflict with another set of
   changes.  In a multi-user calendar system, the calendar client could
   lock an event while the user is editing the event, and unlock the
   event when the user finishes or cancels.  Locks can also be used to
   prevent changes while data is being reorganized.  For example, a
   calendar client might lock two calendar collections prior to moving a
   bunch of calendar resources from one to another.

   Clients may request a lock timeout period that is appropriate to the
   use case.  When the user explicitly decides to reserve a resource and
   prevent other changes, a long timeout might be appropriate, but in
   cases when the client automatically decides to lock the resource the
   timeout should be short (and the client can always refresh the lock
   should it need to).  A short lock timeout means that if the client is
   unable to remove the lock, the other calendar users aren't prevented
   from making changes.

7.4  Finding calendars

   Much of the time a calendar client (or agent) will discover a new
   calendar's location by being provided directly with the URL.  E.g. a
   user will type his or her own calendar location into client
   configuration information, or cut and paste a URL from email into the
   calendar application.  The client need only confirm that the URL
   points to a resource which is a calendar.  The client may also be
   able to browse WebDAV collections to find calendar collections.

   The choice of HTTP URLs means that calendar object resources are
   backward compatible with existing software, but does have the
   disadvantage that existing software does not usually know to look at
   the OPTIONS response to that URL to determine what can be done with
   it.  This is somewhat of a barrier for WebDAV usage as well as with
   CalDAV usage.  This specification does not offer a way through this
   other than making the information available in the OPTIONS response
   should this be requested.




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   For calendar sharing and scheduling use cases, one might wish to find
   the calendar belonging to another user.  If the other user has a
   calendar in the same repository, that calendar can be found by using
   the principal namespace required by WebDAV ACL support.  For other
   cases, the authors have no universal solution but implementors can
   consider whether to use vCard [13] or LDAP [12] standards together
   with calendar attributes [14].












































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8.  XML Element Definitions

8.1  CALDAV:calendar-query XML Element

   Name: calendar-query

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Defines a report for querying calendar data

   Description: See Section 6.4.


   <!ELEMENT calendar-query (DAV:allprop | DAV:propname | DAV:prop)?
                            calendar-data? filter>


8.2  CALDAV:calendar-data-only XML Element

   Name: calendar-data-only

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies that only calendar object resources may be
      contained in a calendar collection.

   Description: The CALDAV:calendar-data-only element MUST be specified
      in the CALDAV:calendar-restrictions property of calendar
      collection that only provide support for calendar object
      resources.



   <!ELEMENT calendar-data-only EMPTY>



8.3  CALDAV:calendar-data XML Element

   Name: calendar-data

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Used to define which parts of a calendar component object
      should be returned by the report that uses this element.






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   Description: When used in a request, the CALDAV:calendar-data element
      specifies the iCalendar components and properties to be returned
      in the iCalendar objects part of the response.  If this element
      doesn't contain any CALDAV:comp element, iCalendar objects will be
      returned with all their components and properties.

   Value: When used inside a response, the CALDAV:calendar-data element
      contains an iCalendar object that matched the search filter
      specified in the request.


   <!ELEMENT calendar-data ((comp?, (expand-recurrence-set |
                                     limit-recurrence-set)?) |
                             #PCDATA)?>

   <!ATTLIST calendar-data content-type CDATA "text/calendar">

   <!ATTLIST calendar-data version CDATA "2.0">


8.3.1  CALDAV:comp XML Element

   Name: comp

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Defines which component types to return

   Description: The name value is a calendar component name (e.g.,
      "VEVENT")

   NOTE: The CALDAV:prop and CALDAV:allprop elements used here have the
   same name as elements defined in WebDAV.  However, the elements used
   here have the "urn:ietf:params:xml:ns:caldav" namespace, as opposed
   to the "DAV:" namespace used for elements defined in WebDAV.

   <!ELEMENT comp ((allcomp, (allprop | prop*)) |
                    (comp*, (allprop | prop*)))>

   <!ATTLIST comp name CDATA #REQUIRED>


8.3.2  CALDAV:allcomp XML Element








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   Name: allcomp

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies that all components shall be returned

   Description: This element can be used when the client wants all types
      of components returned by a report.


   <!ELEMENT allcomp EMPTY>


8.3.3  CALDAV:allprop XML Element

   Name: allprop

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies that all properties shall be returned.

   Description: This element can be used when the client wants all
      properties of components returned by a report.

   NOTE: The CALDAV:allprop element defined here has the same name as
   the DAV:allprop element defined in WebDAV.  However, the CALDAV:
   allprop element defined here uses the "urn:ietf:params:xml:ns:caldav"
   namespace, as opposed to the "DAV:" namespace used for the DAV:
   allprop element defined in WebDAV.

   <!ELEMENT allprop EMPTY>


8.3.4  CALDAV:prop XML Element

   Name: prop

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Defines which properties to return in the response.

   Description: The "name" attribute specifies the name of the calendar
      property to return (e.g., "ATTENDEE").  The "novalue" attribute
      can be used by clients to request that the actual value of the
      property not be returned (if the "novalue" attribute is set to
      "yes").  In that case the server will return just the iCalendar
      property name and any iCalendar parameters and a trailing ":"
      without the subsequent value data.



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   NOTE: The CALDAV:prop element defined here has the same name as the
   DAV:prop element defined in WebDAV.  However, the CALDAV:prop element
   defined here uses the "urn:ietf:params:xml:ns:caldav" namespace, as
   opposed to the "DAV:" namespace used for the DAV:prop element defined
   in WebDAV.

   <!ELEMENT prop EMPTY>

   <!ATTLIST prop name CDATA #REQUIRED
                  novalue (yes|no) "no">


8.3.5  CALDAV:expand-recurrence-set XML Element

   Name: expand-recurrence-set

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Forces the server to expand recurring components into
      separate instances.

   Description: The CALDAV:expand-recurrence-set element specifies that
      recurring components shall be returned as individual components
      with no recurrence properties (i.e., EXDATE, EXRULE, RDATE and
      RRULE).  The required "start" and "end" attributes contain
      iCalendar format DATE-TIME (always specified in UTC) or DATE
      values that define the time interval over which the recurrence
      expansion should take place.  The start value is inclusive and the
      end value is exclusive of the interval as per iCalendar DTSTART
      and DTEND properties.  The server MUST return only those expanded
      components whose time interval intersects the interval specified
      by the start and end attributes.


   <!ELEMENT expand-recurrence-set EMPTY>
   <!ATTLIST expand-recurrence-set start CDATA #REQUIRED
                                   end CDATA #REQUIRED>


8.3.6  CALDAV:limit-recurrence-set XML Element

   Name: limit-recurrence-set

   Namespace: urn:ietf:params:xml:ns:caldav







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   Purpose: Specifies a time range to limit the set of recurrence
      instances returned by the server.

   Description: The CALDAV:limit-recurrence-set XML element specifies
      that a server MUST only return information about the recurrence
      instances whose scheduled time intersect a specified time range
      for a given calendaring REPORT request.  The required "start" and
      "end" attributes specify DATE or DATE-TIME iCalendar values in UTC
      that defines the actual time range.  The server MUST use the same
      logic as defined for CALDAV:time-range to determine if a
      recurrence instance intersect a given time range.

   Definition:

       <!ELEMENT limit-recurrence-set EMPTY>
       <!ATTLIST limit-recurrence-set start CDATA #REQUIRED
                                      end CDATA #REQUIRED>


8.4  CALDAV:filter XML Element

   Name: filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Determines which matching components are returned.

   Description: The "filter" element specifies the search filter used to
      match components that should be returned by a report.


   <!ELEMENT filter comp-filter>


8.4.1  CALDAV:comp-filter XML Element

   Name: comp-filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Limits the search to only the chosen component types.

   Description: The "name" attribute is a calendar component type (e.g.,
      "VEVENT").  When this element is present, the server should only
      return a component if it matches the filter, which is to say:






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   ("no is-defined element" OR "is-defined matches") AND
   ("no time-range element" OR "time-range matches") AND
   ("no sub-component filter" OR "all sub-component filters match") AND
   ("no property filter elements" OR "all property filters match")


   <!ELEMENT comp-filter (is-defined | time-range)?
                         comp-filter* prop-filter*>

   <!ATTLIST comp-filter name CDATA #REQUIRED>


8.4.2  CALDAV:prop-filter XML Element

   Name: prop-filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Limits the search to specific properties.

   Description: The "name" attribute MUST contain an iCalendar property
      name (e.g., "ATTENDEE").  When the CALDAV:prop-filter executes, a
      property matches if:

   ("no is-defined element" OR "is-defined matches") AND
   ("no time-range element" OR "time-range matches") AND
   ("no text match element" OR "text-match matches") AND
   ("no parameter filter elements" OR "all parameter filters match")


   <!ELEMENT prop-filter (is-defined | time-range | text-match)?
                           param-filter*>

   <!ATTLIST prop-filter name CDATA #REQUIRED>


8.4.3  CALDAV:param-filter XML Element

   Name: param-filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Limits the search to specific parameters.

   Description: The "param-filter" element limits the search result to
      the set of resources containing properties with parameters that
      meet the parameter filter rules.  When this filter executes, a
      parameter matches if:



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   ("is-defined matches" OR "text-match matches")


   <!ELEMENT param-filter (is-defined | text-match) >

   <!ATTLIST param-filter name CDATA #REQUIRED>


8.4.4  CALDAV:is-defined XML Element

   Name: is-defined

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Causes a search to match a resource if a component type,
      property or parameter name exists.

   Description: The CALDAV:is-defined XML element limits the filter to
      resources where the named component, property or parameter is
      defined.


   <!ELEMENT is-defined EMPTY>


8.4.5  CALDAV:text-match XML Element

   Name: text-match

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies a substring match on a property or parameter
      value.

   Description: The specified text is used for a substring match against
      the property or parameter value specified in a report.  The
      "caseless" attribute indicates whether the match is case-sensitive
      (value set to "no") or case-insensitive (value set to "yes").  The
      default value is server-specified.  Caseless matching SHOULD be
      implemented as defined in section 5.18 of the Unicode Standard
      ([11]).  Support for the "caseless" attribute is optional.  A
      server should respond with a status of 422 if it is used but
      cannot be supported.


   <!ELEMENT text-match #PCDATA>

   <!ATTLIST text-match caseless (yes|no)>



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8.5  CALDAV:time-range XML Element

   Name: time-range

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies a time interval for testing components against.

   Description: The CALDAV:time-range element allows for a single time
      range to be defined, in order to limit all the results of the
      search to the set of resources that contain a component which
      overlap that time range.  The value of the "start" and "end"
      attributes MUST follow the syntax of the DATE or DATE-TIME
      iCalendar value type, with any time specified in UTC.  While the
      "start" and "end" attributes are not required to allow time ranges
      opened at one end, at least one of them MUST be specified in the
      CALDAV:time-range element.

      [[Comment.2: We need to clarify the logic when the DTSTART, DTEND,
      DURATION, or DUE properties are not defined in the calendar
      component. --desruisseaux]]

      A VEVENT component overlaps a given time-range if:

   (DTSTART <= start AND DTEND > start) OR
   (DTSTART <= start AND DTSTART+DURATION > start) OR
   (DTSTART >= start AND DTSTART < end) OR
   (DTEND   > start AND DTEND <= end)

      A VTODO component overlaps a given time-range if:

   (DTSTART <= start AND DUE >= start) OR
   (DTSTART <= start AND DTSTART+DURATION > start) OR
   (DTSTART >= start AND DTSTART < end) OR
   (DUE     >= start AND DUE < end)

      A VJOURNAL component overlaps a given time-range if:

   DTSTART >= start AND DTSTART < end

      A VALARM component overlaps a given time-range if:

   trigger-time >= start AND trigger-time < end








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      Any property of value type DATE-TIME or DATE (e.g., DTSTAMP) will
      match a given time-range if:

   value >= start AND value < end


   <!ELEMENT time-range EMPTY>

   <!ATTLIST time-range start CDATA
                        end CDATA>


8.6  DAV:response XML Element

   Name: response

   Namespace: DAV:

   Purpose: Response that includes calendar data.

   Description: Modifies the standard WebDAV response element to include
      calendar data in the response if required by the report type.


   <!ELEMENT DAV:response (DAV:href,
                           ((DAV:href*, DAV:status)|(DAV:propstat+)),
                           calendar-data?,
                           DAV:responsedescription?) >


8.7  CALDAV:calendar-multiget XML Element

   Name: calendar-multiget

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: CalDAV report used to retrieve specific calendar component
      items via their URIs.

   Description: See Section 6.5.


   <!ELEMENT calendar-multiget (DAV:allprop | DAV:propname | DAV:prop)?
                           calendar-data? DAV:href+>







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8.8  CALDAV:free-busy-query XML Element

   Name: free-busy-query

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: CalDAV report used to generate a VFREEBUSY to determine busy
      time over a specific set of time ranges.

   Description: See Section 6.6.


   <!ELEMENT free-busy-query time-range+ >






































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9.  Internationalization Considerations


















































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10.  Security Considerations

   HTTP protocol transactions are sent in the clear over the network
   unless protection from snooping is negotiated.  This can be
   accomplished by use of TLS as defined in RFC2818 [6].  In particular,
   HTTP Basic authentication MUST NOT be used unless TLS is in effect.

   Servers MUST take adequate precautions to ensure malicious clients
   cannot consume excessive server resources (CPU, memory, disk, etc.)
   through carefully crafted reports.  For example, a client could
   upload an event with a recurrence rule that specifies a recurring
   event occurring every second for the next 100 years which would
   result in approximately 3 x 10^9 instances!  A report that asks for
   recurrences to be expanded over that range would likely constitute a
   denial-of-service attack on the server.

   [[Comment.3: We should make an explicit reference to the security
   considerations mentionned in iCalendar, iTIP and iMIP.
   --desruisseaux]]
































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11.  IANA Consideration

   In addition to the namespaces defined by RFC2518 [4] for XML
   elements, this document uses a URN to describe a new XML namespace
   conforming to a registry mechanism described in RFC3688 [8].  All
   other IANA considerations mentioned in RFC2518 [4] also apply to this
   document.

11.1  Namespace Registration

   Registration request for the CalDAV namespace:

   URI: urn:ietf:params:xml:ns:caldav

   Registrant Contact: See the "Author's Address" section of this
   document.

   XML: None.  Namespace URIs do not represent an XML specification.

































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12.  Acknowledgements

   The authors would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Michael Arick, Mario Bonin, Chris Bryant, Scott Carr, Mike Douglass,
   Helge Hess, Dan Mosedale, Kervin L. Pierre, Julian F. Reschke, Mike
   Shaver, Simon Vaillancourt, and Jim Whitehead.

   The authors would also like to thank the Calendaring and Scheduling
   Consortium for advice with this specification, and for organizing
   interoperability testing events to help refine it.








































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13.  References

13.1  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
         RFC 2246, January 1999.

   [3]   Dawson, F. and Stenerson, D., "Internet Calendaring and
         Scheduling Core Object Specification (iCalendar)", RFC 2445,
         November 1998.

   [4]   Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
         Jensen, "HTTP Extensions for Distributed Authoring -- WEBDAV",
         RFC 2518, February 1999.

   [5]   Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
         Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
         HTTP/1.1", RFC 2616, June 1999.

   [6]   Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [7]   Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J.
         Whitehead, "Versioning Extensions to WebDAV (Web Distributed
         Authoring and Versioning)", RFC 3253, March 2002.

   [8]   Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
         January 2004.

   [9]   Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
         Distributed Authoring and Versioning (WebDAV) Access Control
         Protocol", RFC 3744, May 2004.

   [10]  Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F.
         Yergeau, "Extensible Markup Language (XML) 1.0 (Third
         Edition)", W3C REC-xml-20040204, February 2004,
         <http://www.w3.org/TR/2004/REC-xml-20040204>.

   [11]  The Unicode Consortium, "The Unicode Standard - Version 4.0",
         Addison-Wesley , August 2003,
         <http://www.unicode.org/versions/Unicode4.0.0/>.

         ISBN 0321185781






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13.2  Informative References

   [12]  Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
         Access Protocol (v3)", RFC 2251, December 1997.

   [13]  Dawson, F. and T. Howes, "vCard MIME Directory Profile",
         RFC 2426, September 1998.

   [14]  Small, T., Hennessy, D., and F. Dawson, "Calendar Attributes
         for vCard and LDAP", RFC 2739, January 2000.


Authors' Addresses

   Cyrus Daboo
   ISAMET Inc.
   5001 Baum Blvd.
   Suite 650
   Pittsburgh, PA  15213
   US

   Email: daboo@isamet.com
   URI:   http://www.isamet.com/


   Bernard Desruisseaux
   Oracle Corporation
   600 Blvd. de Maisonneuve West
   19th Floor
   Montreal, QC  H3A 3J2
   CA

   Email: bernard.desruisseaux@oracle.com
   URI:   http://www.oracle.com/


   Lisa Dusseault
   Open Source Application  Foundation
   2064 Edgewood Dr.
   Palo Alto, CA  94303
   US

   Email: lisa@osafoundation.org
   URI:   http://www.osafoundation.org/







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Appendix A.  CalDAV Method Privilege Table (Normative)

   The following table extend the WebDAV Method Privilege Table
   specified in Appendix B of WebDAV ACL [9].

   +---------------------------------+---------------------------------+
   | METHOD                          | PRIVILEGES                      |
   +---------------------------------+---------------------------------+
   | MKCALENDAR                      | DAV:bind                        |
   |                                 |                                 |
   | REPORT                          | DAV:read or                     |
   |                                 | CALDAV:read-free-busy (on all   |
   |                                 | referenced resources)           |
   +---------------------------------+---------------------------------+





































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Appendix B.  Changes

B.1  Changes in -07

   a.  Various editorial changes.

   b.  Added properties calendar-restrictions and calendar-component-
       restriction-set on calendar collections.

   c.  Added properties calendar-home-URL and calendar-address-set on
       principal resources.

   d.  Removed property calendar-URL on principal resources.

   e.  Added pre- and postconditions to reports.

   f.  Added new XML elements calendar-data-only and limit-recurrent-
       set.

   g.  Modified calendar-data XML element to support the attributes
       content-type and version.

   h.  Reorganised sections 3, 4, 5 & 6 into two sections and re-ordered
       sub-sections.

   i.  Added comment about client not setting a duplicate displayname.

   j.  Removed three CalDAV OPTIONS requests.

   k.  Changed "authenticated user" to "user" in various places.

   l.  Rewrote section on calendar object resource restrictions for
       better clarity.


B.2  Changes in -06

   a.  Reworded section "Recurrence and the Data Model".

   b.  Removed timezone collection feature.

   c.  Removed ability for a server to return the Location header on a
       successful PUT request.

   d.  Clarified restrictions on calendar object resources contained in
       calendar collections.





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   e.  Added preconditions on PUT in calendar collections.

   f.  Added informative "Guidelines" section, with information on
       locking and how to find calendar collections.

   g.  Moved "Sychronization Operations" section in the "Guidelines"
       section.


B.3  Changes in -05

   a.  Removed a lot of non-normative text.

   b.  Removed property promotion/demotion requirements.

   c.  Removed calendar-owner and cal-scale properties.

   d.  Removed 'ical' prefix/text from element names.

   e.  Relaxed WebDAV Class 2 (locking) requirement to a MAY.

   f.  Relaxed MKCALENDAR requirement to a SHOULD.

   g.  Moved the XML Namespace section in the Introduction.

   h.  Added CALDAV: prefix to CalDAV XML elements in the text.

   i.  Added CALDAV:calendar-multiget report.

   j.  Added CALDAV:free-busy-query report.

   k.  Added CALDAV:calendar-description property.

   l.  Changed CALDAV:calendar-query-result element name to CALDAV:
       calendar-data

   m.  Added description and examples of handling timezones.

   n.  Added mandatory "start" and "end" attributes to the CALDAV:
       expand-recurrence-set element.

   o.  Added three CalDAV OPTIONS requests.

   p.  Grouped XML Element declarations in a separate section.







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B.4  Changes in -04

   a.  Added a note about the HTTP Location response header.

   b.  Added report calendar-query.

   c.  Removed reports calendar-property-search and calendar-time-range.

   d.  Removed section on CalDAV and timezones.

   e.  Added requirement to return ETag on creation.

   f.  Revised data model to remove sub-collections from calendar
       collection.

   g.  Added informative references section.

   h.  Removed dependencies on DASL.


B.5  Changes in -03

   a.  Removed Calendar Containers (simplification that doesn't seem to
       remove much functionality)

   b.  Added MKCALENDAR to create calendars and all sub-collections

   c.  Added cal-scale property to calendars


B.6  Changes in -02

   Basically still adding major sections of content:

   a.  Defined new field values to the OPTIONS "DAV:" response header

   b.  Added new resource properties

   c.  Added new principal properties

   d.  Added new SCHEDULE method and related headers

   e.  Added new privileges for scheduling


B.7  Changes in -01





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   a.  Added section on privileges for calendaring, extending WebDAV ACL
       privilege set

   b.  Defined what to do with unrecognized properties in the bodies of
       iCalendar events, with respect to property promotion/demotion














































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