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

Network Working Group                                           N. Freed
Internet-Draft                                                  S. Vedam
Expires: April 27, 2008                                 Sun Microsystems
                                                        October 25, 2007


 Sieve Email Filtering:  Representing Sieves and display directives in
                                  XML
                      draft-freed-sieve-in-xml-00

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on April 27, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

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



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   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.


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  . . . . . . . . . . . . . . . . . . . 12
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Schema for Sieves in XML  . . . . . . . . . . . . . . 13
   Appendix B.  Stylesheet for conversion from XML  . . . . . . . . . 16
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
   Intellectual Property and Copyright Statements . . . . . . . . . . 23




























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1.  Introduction

   Sieve [I-D.ietf-sieve-3028bis] 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.

   Several Sieve extensions have already been specified [RFC3431]
   [RFC3598] [RFC3685] [RFC3934] 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
   convert from normal Sieve format to XML only requires changes when



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   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 [I-D.ietf-sieve-3028bis], 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 arguments, 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.

   Here are some examples of Sieve tests.  Note that such tests have to



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   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:

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



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  <control name="if"><test name="true"/><control name="stop"/></control>

   The example Sieve actions shown about 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 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 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:













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   <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>

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
   group separately and manage things via these groupings.  Some
   examples include Sieve statementss 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
   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.



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   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 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 an any number of arbitrary child
   elements.  Implementations MAY use this 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 presered in structured comments when converted.


5.  Extended Example

   The example sieve script given in section 9 of
   [I-D.ietf-sieve-3028bis] would be represented in XML as follows:

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

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




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     <!--
       Handle messages from known mailing lists
       Move messages from IETF filter discussion list to filter mailbox
     -->
     <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> <!-- move to "filter" mailbox -->
     </control>

     <!--
       Keep all messages to or from people in my company
     -->
     <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>

     <!--
       Try and catch unsolicited email.  If a message is not to me,
       or it contains a subject known to be spam, file it away.
     -->
     <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>



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         </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">
       <!-- Move all other (non-company) mail to "personal"
            mailbox. -->
       <action name="fileinto">
         <str>personal</str>
       </action>
     </control>

   </sieve>

   The same script could be annotated with grahical display hints in
   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>
         </test>
         <action name="fileinto">
           <str>filter</str>
         </action>
       </control>
     </displayblock>

     <displayblock name="Keep all company mail" order="2"



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

     <displayblock name="File noncompany mail as personal" order="4"
                   group="FILE_TO_FOLDER" enable="true">



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       <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>


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] discussses these risks



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   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

   [I-D.ietf-sieve-3028bis]
              Guenther, P. and T. Showalter, "Sieve: An Email Filtering
              Language", draft-ietf-sieve-3028bis-12 (work in progress),
              February 2007, <http://www.ietf.org/internet-drafts/
              draft-ietf-sieve-3028bis-12.txt>.

   [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.

7.2.  Informative References

   [RFC3431]  Segmuller, W., "Sieve Extension: Relational Tests",
              RFC 3431, December 2002.

   [RFC3598]  Murchison, K., "Sieve Email Filtering -- Subaddress
              Extension", RFC 3598, September 2003.

   [RFC3685]  Daboo, C., "SIEVE Email Filtering: Spamtest and VirusTest
              Extensions", RFC 3685, February 2004.

   [RFC3934]  Wasserman, M., "Updates to RFC 2418 Regarding the
              Management of IETF Mailing Lists", BCP 94, RFC 3934,
              October 2004.


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"?>




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   <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:choice>
         </xsd:sequence>
       </xsd:complexType>
     </xsd:element>

     <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: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:choice>
       </xsd:sequence>
       <xsd:attribute use="required" name="name" type="identifier"/>
     </xsd:complexType>

     <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:choice>



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           <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"/>
             <xsd:element ref="displayblock"/>
             <xsd:element ref="displaydata"/>
           </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>



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     </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 -->

     <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>



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         </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>
           <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, '  ')"/>



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             </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>

     <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"/>



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           <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"/>
       <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>



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       <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">
       <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>



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       <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.


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





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   Srinivas Saisatish Vedam
   Sun Microsystems

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














































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   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
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   The IETF takes no position regarding the validity or scope of any
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   The IETF invites any interested party to bring to its attention any
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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