[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 RFC 5784

Network Working Group                                           N. Freed
Internet-Draft                                                  S. Vedam
Expires: August 28, 2008                                Sun Microsystems
                                                       February 25, 2008


      Sieve Email Filtering:  Sieves and display directives in XML
                      draft-freed-sieve-in-xml-01

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
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 28, 2008.

Abstract

   This document describes a way to represent Sieve email filtering
   language scripts in XML.  Representing sieves in XML is intended not
   as an alternate storage format for Sieve but rather as a means to
   facilitate manipulation of scripts using XML tools.

   The XML representation also defines additional elements that have no
   counterparts in the regular Sieve language.  These elements are
   intended for use by graphical user interfaces and provide facilities
   for labeling or grouping sections of a script so they can be
   displayed more conveniently.  These elements are represented as
   specially structured comments in regular Sieve format.




Freed & Vedam            Expires August 28, 2008                [Page 1]


Internet-Draft       An XML Representation for Sieve       February 2008


Change History (to be removed prior to publication as an RFC

   Changed representation of comments in XML to use a comment element.

   Updatde references.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  4
   3.  Grammatical structure of Sieve . . . . . . . . . . . . . . . .  4
   4.  XML Representation of Sieve  . . . . . . . . . . . . . . . . .  5
     4.1.  XML Display Directives . . . . . . . . . . . . . . . . . .  7
   5.  Extended Example . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Schema for Sieves in XML  . . . . . . . . . . . . . . 14
   Appendix B.  Stylesheet for conversion from XML  . . . . . . . . . 16
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
   Intellectual Property and Copyright Statements . . . . . . . . . . 23



























Freed & Vedam            Expires August 28, 2008                [Page 2]


Internet-Draft       An XML Representation for Sieve       February 2008


1.  Introduction

   Sieve [RFC5228] is a language for filtering email messages at or
   around the time of final delivery.  It is designed to be
   implementable on either a mail client or mail server.  It is meant to
   be extensible, simple, and independent of access protocol, mail
   architecture, and operating system and it is intended to be
   manipulated by a variety of different user interfaces.

   Some user interface environments have extensive existing facilities
   for manipulating material represented in XML.  While adding support
   for alternate data syntaxes may be possible in most if not all of
   these environments, it may not be particularly convenient to do so.
   The obvious way to deal with this issue is to map sieves into XML,
   possibly on a separate backend system, manipulate the XML, and
   convert it back to normal Sieve format.

   The fact that conversion into and out of XML may be done as a
   separate operation on a different system argues strongly for defining
   a common XML representation for Sieve.  This way different front end
   user interfaces can be used with different back end mapping and
   storage facilities.

   Another issue with the creation and manipulation of sieve scripts by
   user interfaces is that the language is strictly focused on
   describing email filtering operations.  The language contains no
   mechanisms for indicating how a given script should be presented in a
   user interface.  Such information can be represented in XML very
   easily so it makes sense to define a framework to do this as part of
   the XML format.  Structured comments can then be used to retain this
   information when the script is converted to normal Sieve format.

   Various sieve extensions have already been defined, e.g., [RFC5229]
   [RFC5230] [RFC5231] [RFC5232] [RFC5233] [RFC5235], and many more are
   planned.  The set of extensions available varies from one
   implementation to the next and may even change as a result of
   configuration choices.  It is therefore essential that the XML
   representation of Sieve be able to accommodate Sieve extensions
   without requiring schema changes.  It is also desirable that Sieve
   extensions not require changes to the code that converts to and from
   the XML representation.

   This specification defines an XML representation for sieve scripts
   and explains how the conversion process to and from XML works.  The
   XML representation is capable of accommodating any future Sieve
   extension as long as the underlying Sieve grammar remains unchanged.
   Furthermore, code that converts from XML to the normal Sieve format
   requires no changes to accommodate extensions, while code used to



Freed & Vedam            Expires August 28, 2008                [Page 3]


Internet-Draft       An XML Representation for Sieve       February 2008


   convert from normal Sieve format to XML only requires changes when
   new control commands are added - a rare event.  An XML Schema and
   sample code to convert to and from XML format are also provided in
   the appendices.


2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


3.  Grammatical structure of Sieve

   The Sieve language is designed to be highly extensible without making
   any changes to the basic language syntax.  Accordingly the syntax of
   Sieve, defined in section 8 of [RFC5228], is entirely structural in
   nature and employs no reserved words of any sort.

   Structurally a sieve script consists of a series of commands.  Each
   command in turn consists of an identifier, zero or more arguments, a
   optional test or test-list, and finally an optional block containing
   another series of commands.  Commands are further broken down into
   controls and actions, although this distinction cannot be determined
   from the grammar.

   Some example Sieve controls are:

   stop;               <-- No arguments, test, or command block
   require "fileinto"; <-- Control with a single argument
   if true {stop;}     <-- Control with test and command block

   Some examples of Sieve actions are:

   discard;            <-- Action with no args, test, or command block
   fileinto "folder";  <-- Action with an argument

   At the time of this writing there are no controls defined that accept
   both arguments and a test.  Similarly, there are currently no defined
   actions that allow either a test or a command block.  Nevertheless,
   the Sieve grammar allows such constructs to be defined by some future
   extension.

   A test consists of an identifier followed by zero or more arguments,
   then another test or test-list.  Unlike commands, tests cannot be
   followed by a command block.




Freed & Vedam            Expires August 28, 2008                [Page 4]


Internet-Draft       An XML Representation for Sieve       February 2008


   Here are some examples of Sieve tests.  Note that such tests have to
   appear as part of a command in order to be syntactically valid:

   true                <-- Test with no argument or subordinate test
   header "to" "me@example.com" <-- Test with several arguments

   Command or test arguments can be either string lists, whole numbers
   or tags.  (Tags are simply identifiers preceded by a colon.)  Note
   that although the Sieve grammar treats single strings as a degenerate
   case of a string list, some tests or actions have arguments that can
   only be individual strings, not lists.

   Here is an example showing the use of both a test-list and a string
   list:

   if anyof (not exists ["From", "Date"],
             header :contains "from" "fool@example.edu") {
     discard;
   }

   Extensions can add new controls, actions, tests, or new arguments to
   existing controls or actions.  Extensions can also change how string
   content is interpreted, although this is not relevant to this
   specification.  However, it is especially important to note that so
   far no Sieve extension has added a new control to the language and it
   seems safe to assume that due to their nature future addition of
   controls will be rare.

   Finally, comments are allowed between lexical elements in a Sieve
   script.  It is very important that comments be preserved in the XML
   representation.


4.  XML Representation of Sieve

   Sieve controls and actions are represented in XML as control or
   action elements respectively.  The command's identifier appears as a
   name attribute on the element itself.  This is the only attribute
   allowed on controls and actions - arguments, tests, test-lists, and
   nest command blocks are all represented as nested elements.  While
   naming the element after the control or action itself may seem like a
   better choice, doing so would result in extensions changing the XML
   schema.

   The example Sieve controls shown in the previous section would be
   represented in XML as:





Freed & Vedam            Expires August 28, 2008                [Page 5]


Internet-Draft       An XML Representation for Sieve       February 2008


   <control name="stop"/>
   <control name="require"><str>fileinto</str></control>
   <control name="if">
     <test name="true"/><control name="stop"/>
   </control>

   The example Sieve actions shown above would appear in XML as:

   <action name="discard"/>
   <action name="fileinto"><str>folder</str></action>

   The separation of controls from actions in the XML representation
   means that conversion from normal Sieve format to XML has to be able
   to distinguish between controls and actions.  This is easily done by
   maintaining a list of all known controls since experience indicates
   new controls are rarely added.

   Tests are represented in the same basic way as controls and actions,
   that is, as a test element with a name attribute giving the test
   identifier.  For example:

   <test name="true"/>
   <test name="header"/><str>to</str><str>me@example.com</str></test>

   String, number, and tag arguments are represented as str, num, and
   tag elements respectively.  The actual string, number, or tag
   identifier appears as text inside the element.  None of these
   elements have any defined attributes.  Several examples of arguments
   have already appeared in the preceding control, action and test
   examples.

   String list arguments are represented as a list element which in turn
   contains one or more str elements.  Note that this allows the
   distinction between a single string and a string list containing a
   single string to be preserved.  This is not essential since a list
   containing a single string could simply be mapped to a string, but it
   seems prudent to maintain the distinction when mapping to and from
   XML.

   Nested command blocks appear as a series of control or action
   elements inside of an outer control or action element.  No block
   element is needed since an inner command block can only appear once
   and only after any arguments, tests, or test-lists.  For example:








Freed & Vedam            Expires August 28, 2008                [Page 6]


Internet-Draft       An XML Representation for Sieve       February 2008


   <control name="if>
     <test name="anyof">
       <test name="not">
         <test name="exists>
           <list><str>From</str><str>Date</str></list>
         </test>
       </test>
       <test name="header">
         <tag>contains</tag>
         <str>from</str>
         <str>fool@example.edu</str>
       </test>
     </test>
     <action name="discard"/>
   </control>

   Finally, Sieve comments are mapped to a special comment element in
   XML.  XML comments are not used because some XML tools do not make it
   convenient to access comment nodes.

4.1.  XML Display Directives

   Sometimes graphical user interfaces are a convenient way to provide
   sieve management functions to users.  These interfaces typically
   summarize/annotate/group/display sieve script(s) in an intuitive way
   for end users.

   To do this effectively, the graphical user interface may require
   additional information about the sieve script itself.  That
   information or "meta-data" might include, but is not limited to - a
   sieve name (identifying the current sieve), whether the sieve is
   enabled or disabled, the order in which the part of the sieve are
   presented to the user.  The graphical user interface may also choose
   to provide mechanisms to allow the user to modify the script.

   It is often useful for a graphical user interface to group related
   sieve script elements and provide an interface that display these
   groups separately so they can be managed as a single object.  Some
   examples include Sieve statements that together provide vacation
   responders, blacklists/whitelists and other types of filtering
   controls.

   Some advanced graphical user interfaces may even provide a natural
   language representation of a sieve script and/or an advanced
   interface to present sieve statements directly to the user.

   A graphical user interface may also choose to support only a subset
   of action commands in the Sieve language (and its extensions) and so



Freed & Vedam            Expires August 28, 2008                [Page 7]


Internet-Draft       An XML Representation for Sieve       February 2008


   a mechanism to indicate the extent of support and characterize the
   relationships between those supported action commands and test (with
   its arguments) is immensely useful and probably required for clients
   that may not have complete knowledge of sieve grammar and semantics.

   The Sieve language contains no mechanisms for indicating how a given
   script should be presented in a user interface.  The language also
   does not contain any specific mechanisms to represent other sorts of
   meta-data about the script.  Providing support for such meta-data as
   part of a sieve script is currently totally implementation specific
   and is usually done by imposing some type of structure on comments.

   However, such information can be represented in XML very easily so it
   makes sense to define a framework to do this as part of the XML
   format.  Implementations may choose to use structured comments to
   retain this information when the script is converted to normal Sieve
   format.

   This XML representation defines two display directives - displayblock
   and displaydata - as containers for meta-data needed by graphical
   user interfaces.

   The displayblock element can be used to enclose any number of sieve
   statements at any level.  It is semantically meaningless to the sieve
   script itself.  It allows an arbitrary set of attributes.
   Implementations MAY use this to provide many simple, display related
   meta-data for the sieve such as sieve identifier, group identifier,
   order of processing, etc.  This information SHOULD be preserved in
   structured comments during conversion of XML to the normal Sieve
   syntax.

   The displaydata element supports any number of arbitrary child
   elements.  Implementations MAY use this to represent complex data
   about that sieve such as a natural language representation of sieve
   or a way to provide the sieve script directly.  Again, this
   information SHOULD be preserved in structured comments when
   converted.


5.  Extended Example

   The example sieve script given in section 9 of [RFC5228] would be
   represented in XML as follows:

   <sieve>
     <comment>
       Example Sieve Filter
       Declare any optional features or extensions used by the script



Freed & Vedam            Expires August 28, 2008                [Page 8]


Internet-Draft       An XML Representation for Sieve       February 2008


     </comment>

     <control name="require">
       <str>fileinto</str>
     </control>

     <comment>
       Handle messages from known mailing lists
       Move messages from IETF filter discussion list to filter mailbox
     </comment>
     <control name="if">
       <test name="header">
         <tag>is</tag>
         <str>Sender</str>
         <str>owner-ietf-mta-filters@imc.org</str>
       </test>
       <action name="fileinto">
         <str>filter</str>
       </action> <comment>move to "filter" mailbox</comment>
     </control>

     <comment>
       Keep all messages to or from people in my company
     </comment>
     <control name="elsif">
       <test name="address">
         <tag>domain</tag>
         <tag>is</tag>
         <list>
           <str>From</str>
           <str>To</str>
         </list>
         <str>example.com</str>
       </test>
       <action name="keep"/>
     </control>

     <comment>
       Try and catch unsolicited email.  If a message is not to me,
       or it contains a subject known to be spam, file it away.
     </comment>
     <control name="elsif">
       <test name="anyof">
         <test name="not">
           <test name="address">
             <tag>all</tag>
             <tag>contains</tag>
             <list>



Freed & Vedam            Expires August 28, 2008                [Page 9]


Internet-Draft       An XML Representation for Sieve       February 2008


               <str>To</str>
               <str>Cc</str>
               <str>Bcc</str>
             </list>
             <str>me@example.com</str>
           </test>
         </test>
         <test name="header">
           <tag>matches</tag>
           <str>subject</str>
           <list>
             <str>*make*money*fast*</str>
             <str>*university*dipl*mas*</str>
           </list>
         </test>
       </test>
       <action name="fileinto">
         <str>spam</str>
       </action>
     </control>
     <control name="else">
       <comment>
         Move all other (non-company) mail to "personal"
         mailbox.
       </comment>
       <action name="fileinto">
         <str>personal</str>
       </action>
     </control>

   </sieve>

   The same script could be annotated with graphical display hints in a
   variety of ways.  Two possibilities are:

   <sieve>

     <control name="require">
       <str>fileinto</str>
     </control>

     <displayblock name="File filter list mail" order="1"
                   group="FILE_TO_FOLDER" enable="true">
       <control name="if">
         <test name="header">
           <tag>is</tag>
           <str>Sender</str>
           <str>owner-ietf-mta-filters@imc.org</str>



Freed & Vedam            Expires August 28, 2008               [Page 10]


Internet-Draft       An XML Representation for Sieve       February 2008


         </test>
         <action name="fileinto">
           <str>filter</str>
         </action>
       </control>
     </displayblock>

     <displayblock name="Keep all company mail" order="2"
                   group="KEEP_MESSAGE" enable="true">
       <control name="elsif">
         <test name="address">
           <tag>domain</tag>
           <tag>is</tag>
           <list>
             <str>From</str>
             <str>To</str>
           </list>
           <str>example.com</str>
         </test>
         <action name="keep"/>
      </control>
     </displayblock>

     <displayblock name="File suspected spam" order="3"
                   group="FILE_TO_FOLDER" enable="true">
        <control name="elsif">
          <test name="anyof">
            <test name="not">
              <test name="address">
                <tag>all</tag>
                <tag>contains</tag>
                <list>
                  <str>To</str>
                  <str>Cc</str>
                  <str>Bcc</str>
                </list>
                <str>me@example.com</str>
              </test>
            </test>
            <test name="header">
              <tag>matches</tag>
              <str>subject</str>
              <list>
                <str>*make*money*fast*</str>
                <str>*university*dipl*mas*</str>
              </list>
            </test>
          </test>



Freed & Vedam            Expires August 28, 2008               [Page 11]


Internet-Draft       An XML Representation for Sieve       February 2008


          <action name="fileinto">
            <str>spam</str>
          </action>
        </control>
      </displayblock>

     <displayblock name="File noncompany mail as personal" order="4"
                   group="FILE_TO_FOLDER" enable="true">
       <control name="else">
         <action name="fileinto">
           <str>personal</str>
         </action>
       </control>
     </displayblock>

   </sieve>

   Note that since displayblock elements are semantically null as far as
   the script itself is concerned they can be used to group structures
   like elsif and else that are tied to statements in other groups.

  <sieve>

    <displaydata>
      <nls-interpretation>
        If the e-mail header "Sender" is owner-ietf-mta-filters@imc.org
        then file it into the "filter" folder.

        Otherwise if the address in the "From" or "To" has a domain
        that is "example.com" then keep it.

        Otherwise  messages meeting with any of these conditions:

        (1) None of the addresses in "To" or "Cc"  or "Bcc" contains
            the domain "example.com".

        (2) The "Subject" field matches the pattern *make*money*fast* or
            *university*dipl*mas* then file  it into the "spam" folder.

        If all else fails then file the message in the "personal"
        folder.
      </nls-interpretation>
     </displaydata>

     ... the actual sieve script ...

  </sieve>




Freed & Vedam            Expires August 28, 2008               [Page 12]


Internet-Draft       An XML Representation for Sieve       February 2008


6.  Security Considerations

   Any syntactically valid sieve script can be represented in XML.
   Accordingly, all security considerations applicable to Sieve and any
   extensions used also apply to the XML representation.

   The use of XML carries its own security risks.  Section 7 of RFC 3470
   [RFC3470] discusses these risks.

   Arbitrary data can be placed in the extensible displayblock and
   displaydata constructs defined in this specification, possibly
   including entire scripts in languages other than Sieve.  Appropriate
   security precautions should be taken when using these facilities.


7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3470]  Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for
              the Use of Extensible Markup Language (XML)
              within IETF Protocols", BCP 70, RFC 3470, January 2003.

   [RFC5228]  Guenther, P. and T. Showalter, "Sieve: An Email Filtering
              Language", RFC 5228, January 2008.

7.2.  Informative References

   [RFC5229]  Homme, K., "Sieve Email Filtering: Variables Extension",
              RFC 5229, January 2008.

   [RFC5230]  Showalter, T. and N. Freed, "Sieve Email Filtering:
              Vacation Extension", RFC 5230, January 2008.

   [RFC5231]  Segmuller, W. and B. Leiba, "Sieve Email Filtering:
              Relational Extension", RFC 5231, January 2008.

   [RFC5232]  Melnikov, A., "Sieve Email Filtering: Imap4flags
              Extension", RFC 5232, January 2008.

   [RFC5233]  Murchison, K., "Sieve Email Filtering: Subaddress
              Extension", RFC 5233, January 2008.

   [RFC5235]  Daboo, C., "Sieve Email Filtering: Spamtest and Virustest
              Extensions", RFC 5235, January 2008.



Freed & Vedam            Expires August 28, 2008               [Page 13]


Internet-Draft       An XML Representation for Sieve       February 2008


Appendix A.  Schema for Sieves in XML

   The following defines a schema for the XML representation of Sieve
   scripts.  Note that aside from defining the displaydata and
   displayblock elements this schema imposes no constraints on their
   content.

   <?xml version="1.0" encoding="UTF-8"?>

   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

     <xsd:element name="sieve">
       <xsd:complexType>
         <xsd:sequence>
           <xsd:choice maxOccurs="unbounded" minOccurs="0">
             <xsd:element ref="control"/>
             <xsd:element ref="action"/>
             <xsd:element ref="displayblock"/>
             <xsd:element ref="displaydata"/>
             <xsd:element ref="comment"/>
           </xsd:choice>
         </xsd:sequence>
       </xsd:complexType>
     </xsd:element>

     <xsd:element name="comment" type="xsd:string"/>

     <xsd:complexType name="command">
       <xsd:sequence>
         <xsd:choice minOccurs="0" maxOccurs="unbounded">
           <xsd:element ref="str"/>
           <xsd:element ref="num"/>
           <xsd:element ref="list"/>
           <xsd:element ref="tag"/>
            <xsd:element ref="comment"/>
         </xsd:choice>
         <xsd:element ref="test" minOccurs="0" maxOccurs="1"/>
         <xsd:choice minOccurs="0" maxOccurs="unbounded">
           <xsd:element ref="control"/>
           <xsd:element ref="action"/>
           <xsd:element ref="displayblock"/>
           <xsd:element ref="displaydata"/>
           <xsd:element ref="comment"/>
         </xsd:choice>
       </xsd:sequence>
       <xsd:attribute use="required" name="name" type="identifier"/>
     </xsd:complexType>



Freed & Vedam            Expires August 28, 2008               [Page 14]


Internet-Draft       An XML Representation for Sieve       February 2008


     <xsd:element name="control" type="command"/>

     <xsd:element name="action" type="command"/>

     <xsd:element name="test">
       <xsd:complexType>
         <xsd:sequence>
           <xsd:choice minOccurs="0" maxOccurs="unbounded">
             <xsd:element ref="str"/>
             <xsd:element ref="num"/>
             <xsd:element ref="list"/>
             <xsd:element ref="tag"/>
             <xsd:element ref="comment"/>
           </xsd:choice>
           <xsd:element ref="test" minOccurs="0"
                        maxOccurs="unbounded"/>
         </xsd:sequence>
         <xsd:attribute use="required" name="name" type="identifier"/>
       </xsd:complexType>
     </xsd:element>

     <xsd:element name="list">
       <xsd:complexType>
         <xsd:sequence>
           <xsd:element ref="str" minOccurs="1"
                        maxOccurs="unbounded"/>
         </xsd:sequence>
       </xsd:complexType>
     </xsd:element>

     <xsd:element name="tag" type="identifier"/>

     <xsd:element name="str" type="xsd:string"/>

     <xsd:element name="num" type="xsd:nonNegativeInteger"/>

     <xsd:simpleType name="identifier">
       <xsd:restriction base="xsd:token">
         <xsd:pattern value="[A-Za-z_][A-Za-z0-9_]*"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:element name="displayblock">
       <xsd:complexType>
         <xsd:sequence>
           <xsd:choice minOccurs="0" maxOccurs="unbounded">
             <xsd:element ref="control"/>
             <xsd:element ref="action"/>



Freed & Vedam            Expires August 28, 2008               [Page 15]


Internet-Draft       An XML Representation for Sieve       February 2008


             <xsd:element ref="displayblock"/>
             <xsd:element ref="displaydata"/>
             <xsd:element ref="comment"/>
           </xsd:choice>
         </xsd:sequence>
         <xsd:anyAttribute processContents="skip"/>
       </xsd:complexType>
     </xsd:element>

     <xsd:element name="displaydata">
       <xsd:complexType>
         <xsd:sequence minOccurs="0" maxOccurs="unbounded">
           <xsd:any processContents="skip"/>
         </xsd:sequence>
       </xsd:complexType>
     </xsd:element>

   </xsd:schema>


Appendix B.  Stylesheet for conversion from XML

   <?xml version="1.0" encoding="UTF-8"?>

   <!-- Convert Sieve in XML to standard Sieve syntax -->

   <xsl:stylesheet version="1.0"
                   xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

     <xsl:output method="text" encoding="UTF-8"
                 media-type="application/sieve"/>

     <!-- Only preserve whitespace in str elements -->
     <xsl:strip-space elements="*"/>
     <xsl:preserve-space elements="str"/>

     <!-- Match top level sieve node,
          start processing in sieve mode -->

     <xsl:template match="sieve">
       <xsl:apply-templates
          select="control|action|comment()|displayblock|displaydata"
          mode="sieve">
         <xsl:with-param name="prefix" select="''"/>
       </xsl:apply-templates>
     </xsl:template>

     <!-- Routine to properly literalize quotes in Sieve strings -->



Freed & Vedam            Expires August 28, 2008               [Page 16]


Internet-Draft       An XML Representation for Sieve       February 2008


     <xsl:template name="quote-string">
       <xsl:param name="str"/>
       <xsl:choose>
         <xsl:when test="not($str)"/>
         <xsl:when test="contains($str, '&quot;')">
           <xsl:call-template name="quote-string">
             <xsl:with-param name="str"
                select="substring-before($str, '&quot;')"/>
           </xsl:call-template>
           <xsl:text>\&quot;</xsl:text>
           <xsl:call-template name="quote-string">
             <xsl:with-param name="str"
                select="substring-after($str, '&quot;')"/>
           </xsl:call-template>
         </xsl:when>
         <xsl:when test="contains($str, '\')">
           <xsl:call-template name="quote-string">
             <xsl:with-param name="str"
                select="substring-before($str, '\')"/>
           </xsl:call-template>
           <xsl:text>\\</xsl:text>
           <xsl:call-template name="quote-string">
             <xsl:with-param name="str"
                select="substring-after($str, '\')"/>
           </xsl:call-template>
         </xsl:when>
         <xsl:otherwise>
           <xsl:value-of select="$str"/>
         </xsl:otherwise>
       </xsl:choose>
     </xsl:template>

     <!-- Sieve mode processing templates -->

     <xsl:template match="control|action" mode="sieve">
       <xsl:param name="prefix"/>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:value-of select="@name"/>
       <xsl:variable name="blockbegin"
               select="generate-id(control|action)"/>
       <xsl:for-each select="*|comment()">
         <xsl:choose>
           <xsl:when test="self::str|self::num|
                           self::list|self::tag|self::test">
             <xsl:apply-templates select="." mode="sieve"/>
           </xsl:when>



Freed & Vedam            Expires August 28, 2008               [Page 17]


Internet-Draft       An XML Representation for Sieve       February 2008


           <xsl:when test="generate-id(.) = $blockbegin">
             <xsl:text xml:space="preserve">
   </xsl:text>
             <xsl:value-of select="$prefix"/>
             <xsl:text>{</xsl:text>
             <xsl:apply-templates select="." mode="sieve">
               <xsl:with-param name="prefix"
                  select="concat($prefix, '  ')"/>
             </xsl:apply-templates>
           </xsl:when>
           <xsl:otherwise>
             <xsl:apply-templates select="." mode="sieve">
               <xsl:with-param name="prefix"
                  select="concat($prefix, '  ')"/>
             </xsl:apply-templates>
           </xsl:otherwise>
         </xsl:choose>
       </xsl:for-each>
       <xsl:choose>
         <xsl:when test="count(control|action) &gt; 0">
           <xsl:text xml:space="preserve">
   </xsl:text>
           <xsl:value-of select="$prefix"/>
           <xsl:text>}</xsl:text>
         </xsl:when>
         <xsl:otherwise>
           <xsl:text>;</xsl:text>
         </xsl:otherwise>
       </xsl:choose>
     </xsl:template>

     <xsl:template match="test" mode="sieve">
       <xsl:text xml:space="preserve"> </xsl:text>
       <xsl:value-of select="@name"/>
       <xsl:apply-templates select="str|num|list|tag|comment()"
                  mode="sieve"/>
       <xsl:if test="count(descendant::test) &gt; 0">
         <xsl:text> (</xsl:text>
         <xsl:for-each select="test">
           <xsl:apply-templates select="." mode="sieve"/>
           <xsl:if test="count(following-sibling::test) &gt; 0">
             <xsl:text>,</xsl:text>
           </xsl:if>
         </xsl:for-each>
         <xsl:text> )</xsl:text>
       </xsl:if>
     </xsl:template>




Freed & Vedam            Expires August 28, 2008               [Page 18]


Internet-Draft       An XML Representation for Sieve       February 2008


     <xsl:template match="str" mode="sieve">
       <xsl:text> &quot;</xsl:text>
       <xsl:call-template name="quote-string">
         <xsl:with-param name="str" select="text()"/>
       </xsl:call-template>
       <xsl:text>&quot;</xsl:text>
     </xsl:template>

     <xsl:template match="num" mode="sieve">
       <xsl:text xml:space="preserve"> </xsl:text>
       <!-- Use numeric suffixes when possible -->
       <xsl:choose>
         <xsl:when test="(number(text()) mod 1073741824) = 0">
           <xsl:value-of select="number(text()) div 1073741824"/>
           <xsl:text>G</xsl:text>
         </xsl:when>
         <xsl:when test="(number(text()) mod 1048576) = 0">
           <xsl:value-of select="number(text()) div 1048576"/>
           <xsl:text>M</xsl:text>
         </xsl:when>
         <xsl:when test="(number(text()) mod 1024) = 0">
           <xsl:value-of select="number(text()) div 1024"/>
           <xsl:text>K</xsl:text>
         </xsl:when>
         <xsl:otherwise>
           <xsl:value-of select="text()"/>
         </xsl:otherwise>
       </xsl:choose>
     </xsl:template>

     <xsl:template match="list" mode="sieve">
       <xsl:text> [</xsl:text>
       <xsl:for-each select="str">
         <xsl:apply-templates select="." mode="sieve"/>
         <xsl:if test="count(following-sibling::str) &gt; 0">
           <xsl:text>,</xsl:text>
         </xsl:if>
       </xsl:for-each>
       <xsl:text> ]</xsl:text>
     </xsl:template>

     <xsl:template match="tag" mode="sieve">
       <xsl:text> :</xsl:text>
       <xsl:value-of select="text()"/>
     </xsl:template>

     <xsl:template match="comment" mode="sieve">
       <xsl:param name="prefix"/>



Freed & Vedam            Expires August 28, 2008               [Page 19]


Internet-Draft       An XML Representation for Sieve       February 2008


       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>/*</xsl:text>
       <xsl:value-of select="."/>
       <xsl:value-of select="$prefix"/>
       <xsl:text>*/</xsl:text>
     </xsl:template>

     <!-- Convert display information into structured comments -->
     <xsl:template match="displayblock" mode="sieve">
       <xsl:param name="prefix"/>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>/* [*</xsl:text>
       <xsl:apply-templates select="@*" mode="copy"/>
       <xsl:text> */</xsl:text>
       <xsl:apply-templates
          select="control|action|comment()|displayblock|displaydata"
          mode="sieve">
         <xsl:with-param name="prefix" select="$prefix"/>
       </xsl:apply-templates>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>/* *] */</xsl:text>
     </xsl:template>

     <xsl:template match="displaydata" mode="sieve">
       <xsl:param name="prefix"/>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>/* [|</xsl:text>
       <xsl:apply-templates mode="copy">
         <xsl:with-param name="prefix"
                         select="concat($prefix, '  ')"/>
       </xsl:apply-templates>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>   |] */</xsl:text>
     </xsl:template>

     <!-- Copy mode processing templates -->

     <xsl:template match="*[not(node())]" mode="copy">



Freed & Vedam            Expires August 28, 2008               [Page 20]


Internet-Draft       An XML Representation for Sieve       February 2008


       <xsl:param name="prefix"/>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>&lt;</xsl:text>
       <xsl:value-of select="name()"/>
       <xsl:apply-templates select="@*" mode="copy"/>
       <xsl:text>/&gt;</xsl:text>
     </xsl:template>

     <xsl:template match="*[node()]" mode="copy">
       <xsl:param name="prefix"/>
       <xsl:text xml:space="preserve">
   </xsl:text>
       <xsl:value-of select="$prefix"/>
       <xsl:text>&lt;</xsl:text>
       <xsl:value-of select="name()"/>
       <xsl:apply-templates select="@*" mode="copy"/>
       <xsl:text>&gt;</xsl:text>
       <xsl:apply-templates mode="copy">
         <xsl:with-param name="prefix"
                         select="concat($prefix, '  ')"/>
       </xsl:apply-templates>
       <xsl:if test="*[last()][not(text())]">
         <xsl:text xml:space="preserve">
   </xsl:text>
         <xsl:value-of select="$prefix"/>
       </xsl:if>
       <xsl:text>&lt;/</xsl:text>
       <xsl:value-of select="name()"/>
       <xsl:text>&gt;</xsl:text>
     </xsl:template>

     <xsl:template match="@*" mode="copy">
       <xsl:text> </xsl:text>
       <xsl:value-of select="name()"/>
       <xsl:text>="</xsl:text>
       <xsl:value-of select="."/>
       <xsl:text>"</xsl:text>
     </xsl:template>

   </xsl:stylesheet>


Appendix C.  Acknowledgements

   The stylesheet copy mode code is loosely based on a sample code
   posted to the xsl-list list by Americo Albuquerque.  Andrew McKeon



Freed & Vedam            Expires August 28, 2008               [Page 21]


Internet-Draft       An XML Representation for Sieve       February 2008


   provided useful comments on the document.


Authors' Addresses

   Ned Freed
   Sun Microsystems
   3401 Centrelake Drive, Suite 410
   Ontario, CA  92761-1205
   USA

   Phone: +1 909 457 4293
   Email: ned.freed@mrochek.com


   Srinivas Saisatish Vedam
   Sun Microsystems

   Phone: +91 80669 27577
   Email: Srinivas.Sv@Sun.COM































Freed & Vedam            Expires August 28, 2008               [Page 22]


Internet-Draft       An XML Representation for Sieve       February 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.











Freed & Vedam            Expires August 28, 2008               [Page 23]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/