xep-0131.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Stanza Headers and Internet Metadata</title>
  <abstract>This specification defines an XMPP protocol extension for representing non-address-related headers in an XML format that is appropriate for use in XMPP. While the protocol provides a flexible mechanism for representing many kinds of standard Internet metadata, a registry of values is defined to structure the possible range of headers, and the inital registration includes headers from email, HTTP, MIME, and SIP.</abstract>
  &LEGALNOTICE;
  <number>0131</number>
  <status>Draft</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0030</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>shim</shortname>
  <schemaloc>
    <url>http://www.xmpp.org/schemas/shim.xsd</url>
  </schemaloc>
  <registry/>
  &stpeter;
  &hildjj;
  <revision>
    <version>1.2</version>
    <date>2006-07-12</date>
    <initials>psa</initials>
    <remark><p>Added Urgency header from registry.</p></remark>
  </revision>
  <revision>
    <version>1.1</version>
    <date>2005-08-19</date>
    <initials>psa</initials>
    <remark><p>Added Date, DateTime, and Time headers conforming to profiles from XEP-0082; renamed Date header to RFC2822Date; added note about date-related headers; added headers from RFC 2413 (Dublin Core).</p></remark>
  </revision>
  <revision>
    <version>1.0</version>
    <date>2004-10-22</date>
    <initials>psa</initials>
    <remark><p>Per a vote of the Jabber Council, advanced status to Draft; also added more headers from RFC 2822 to the initial registry submission.</p></remark>
  </revision>
  <revision>
    <version>0.8</version>
    <date>2004-09-29</date>
    <initials>psa</initials>
    <remark><p>Specified service discovery usage; corrected examples; further specified security considerations.</p></remark>
  </revision>
  <revision>
    <version>0.7</version>
    <date>2004-09-20</date>
    <initials>psa</initials>
    <remark><p>Specified location of headers in IQ stanzas.</p></remark>
  </revision>
  <revision>
    <version>0.6</version>
    <date>2004-07-06</date>
    <initials>psa</initials>
    <remark><p>Added "Store" header.</p></remark>
  </revision>
  <revision>
    <version>0.5</version>
    <date>2004-06-28</date>
    <initials>psa</initials>
    <remark><p>Added "Distribute" header.</p></remark>
  </revision>
  <revision>
    <version>0.4</version>
    <date>2004-05-27</date>
    <initials>psa</initials>
    <remark><p>Added "Classification" header.</p></remark>
  </revision>
  <revision>
    <version>0.3</version>
    <date>2004-05-10</date>
    <initials>psa</initials>
    <remark><p>Added headers from RFCs 2045, 2616, 2617, and 3261 to initial registration.</p></remark>
  </revision>
  <revision>
    <version>0.2</version>
    <date>2004-05-09</date>
    <initials>psa</initials>
    <remark><p>Specified registry process; added headers from RFC 2822 to initial registration; defined "Created" and "TTL" headers.</p></remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2004-03-19</date>
    <initials>psa/jh</initials>
    <remark><p>Initial version.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <p>In order to ensure proper processing by the recipient of an XML stanza, some Jabber protocols and other XMPP extensions may need to enable the sender to communicate non-addressing information about the stanza (this is especially true of protocols that translate from a foreign format to XMPP; a good example is &xep0111;). Such information was formerly included in &xep0033;, but was removed from that specification when it was changed to focus on addressing information only. Therefore, this document defines a mechanism for encapsulating non-addressing "header" information about stanzas, including standard Internet metadata such as that defined by &rfc2045;, &rfc2616;, &rfc2617;, &rfc2822;, and &rfc3261;. Such information is encapsulated in a protocol extension qualified by the 'http://jabber.org/protocol/shim' namespace, where "SHIM" stands for "Stanza Headers and Internet Metadata".</p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
  <p>This protocol addresses the following requirements:</p>
  <ol>
    <li>Enable the inclusion of any header information</li>
    <li>Encapsulate all information in XML</li>
    <li>Ensure interoperability with existing non-XMPP header and metadata formats (HTTP, MIME, SIP, SMTP, etc.)</li>
  </ol>
</section1>
<section1 topic='Discovery' anchor='disco'>
  <section2 topic='Protocol Support' anchor='disco-proto'>
    <p>In order to discover whether another entity supports this protocol, an entity MUST use &xep0030;.</p>
    <example caption='Entity queries another entity regarding protocol support'><![CDATA[
<iq from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
]]></example>
    <example caption='Queried entity communicates protocol support'><![CDATA[
<iq from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='http://jabber.org/protocol/shim'/>
    ...
  </query>
</iq>
]]></example>
  </section2>
  <section2 topic='Header Support' anchor='disco-header'>
    <p>It can be desirable (and, in some contexts, necessary) to determine if the intended recipient of an XML stanza supports a specific header (e.g., the "Classification" header) before sending information that may depend on that header. Therefore, implementations of this protocol MUST advertise which particular SHIM headers they support when queried via disco#info at the well-known service discovery node 'http://jabber.org/protocol/shim'.</p>
    <example caption='Entity queries another entity regarding header support'><![CDATA[
<iq from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='http://jabber.org/protocol/shim'/>
</iq>
]]></example>
    <example caption='Queried entity communicates header support'><![CDATA[
<iq from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='http://jabber.org/protocol/shim'>
    ...
    <feature var='http://jabber.org/protocol/shim#Classification'/>
    <feature var='http://jabber.org/protocol/shim#Distribute'/>
    <feature var='http://jabber.org/protocol/shim#Store'/>
    ...
  </query>
</iq>
]]></example>
    <p>The values of the 'var' attribute MUST be of the form "http://jabber.org/protocol/shim#header", where "header" is to be replaced with the name of the header as registered with the &REGISTRAR; (see below).</p>
  </section2>
</section1>
<section1 topic='Protocol' anchor='protocol'>
  <p>In a fashion similar to the structure of <cite>Extended Stanza Addressing</cite>, headers for &MESSAGE; and &PRESENCE; stanzas are contained in a &lt;headers/&gt; wrapper element qualified by the 'http://jabber.org/protocol/shim' namespace; each header is a child of this wrapper element, and is encapsulated via a &lt;header/&gt; element whose 'name' attribute identifies the header and whose XML character data specifies the relevant value:
    <note>Standard XML escaping rules apply to the XML character data, so that the characters &lt; &gt; &apos; &quot; &amp; MUST be escaped to &amp;lt; &amp;gt; &amp;apos; &amp;quot; &amp;amp; respectively when translating from non-XML protocols (such as MIME and SIP) to SHIM, and the escaped sequences (e.g., &amp;lt;) MUST be transformed to the equivalent non-escaped character (e.g., '&lt;') when translating from SHIM to the non-XML protocol. Escaping and unescaping will normally be performed by a gateway that translates between XMPP and a foreign protocol such as MIME or SIP.</note>
  </p>
  <example caption='A basic example'><![CDATA[
<message from='romeo@montague.net/orchard'
         to='juliet@capulet.com/balcony'>
  <body>Neither, fair saint, if either thee dislike.</body>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='In-Reply-To'>123456789@capulet.com</header>
    <header name='Keywords'>shakespeare,&lt;xmpp/&gt;</header>
  </headers>
</message>
]]></example>
  <p>In accordance with &xmppcore;, an &IQ; stanza must not contain more than one non-error child element; this places constraints on the location of SHIM headers in the XML hierarchy. Specifically, the &lt;headers/&gt; wrapper element MUST NOT be a direct child of &IQ; and instead SHOULD be a grandchild of &IQ; and a direct child of the content-bearing child element of &IQ; (e.g., &QUERY;, <em>not</em> &lt;error/&gt;).</p>
  <example caption='An IQ example'><![CDATA[
<iq from='romeo@montague.net/orchard'
    to='juliet@capulet.com/balcony'
    id='ping1'>
  <query xmlns='jabber:iq:time'>
    <headers xmlns='http://jabber.org/protocol/shim'>
      <header name='Created'>2004-09-21T03:01:52Z</header>
    </headers>
  </query>
</iq>
]]></example>
</section1>
<section1 topic='Header Definitions' anchor='headers'>
  <p>All public headers SHOULD be registered with the XMPP Registrar following the process specified in the <link url="#registrar">XMPP Registrar Considerations</link> section of this document. Many such headers are defined by other protocol specifications, such as RFCs 2045, 2616, 2617, 2822, and 3261; implementors MUST refer to those specifications for definition of the relevant headers.</p>
  <p>This document defines several additional headers that may prove useful within Jabber protocols and other XMPP extensions, as specified in the following sections; further headers may be registered with the XMPP Registrar, either directly or via definition in XMPP Extension Protocol specifications.</p>
  <section2 topic='Classification' anchor='headers-classification'>
    <p>The Classification header enables a sender or other entity to classify a stanza according to some classification scheme. The values of the XML character data contained within this header are out of scope for this document, since they are determined by the using application. Note: This header may be security-sensitive (see the <link url='#security'>Security Considerations</link> for details).</p>
  </section2>
  <section2 topic='Created' anchor='headers-created'>
    <p>The Date header is defined by RFC 2822 and therefore follows the date and time format defined by RFC 2822; while this header is thus useful for translating email messages into XMPP stanzas, it is not consistent with &xep0082;. Therefore we define the "Created" header, which specifies the date and time when a stanza was created by the originating entity, where the value conforms to the DateTime profile specified in XEP-0082.</p>
  </section2>
  <section2 topic='Distribute' anchor='headers-distribute'>
    <p>The Distribute header enables a sender to specify whether the stanza may be further distributed by the recipient to other entities on the network. The allowable values for this header are "true" and "false". If the sender specifies a value of "false", the recipient MUST NOT further distribute the stanza or any information contained therein; if the sender specifies a value of "true", the recipient MAY further distribute the stanza or any information contained therein; if the value is anything other than "true" or "false" and the recipient does not understand the value, the recipient MUST assume the default value of "false". This header is semantically equivalent to the "Distribute" flag defined in &geoprivpol;. (The HTTP "Max-Forwards" header is not appropriate for this usage, since it defines proxy and gateway behavior rather than recipient behavior.) Note: This header may be security-sensitive (see the <link url='#security'>Security Considerations</link> for details).</p>
  </section2>
  <section2 topic='Store' anchor='headers-store'>
    <p>The Store header enables a sender to specify whether the stanza may be stored or archived by the recipient. The allowable values for this header are "true" and "false". If the sender specifies a value of "false", the recipient MUST NOT store the stanza or any information contained therein; if the sender specifies a value of "true", the recipient MAY store the stanza or any information contained therein; if the value is anything other than "true" or "false" and the recipient does not understand the value, the recipient MUST assume the default value of "false". Note: This header may be security-sensitive (see the <link url='#security'>Security Considerations</link> for details).</p>
  </section2>
  <section2 topic='TTL' anchor='headers-ttl'>
    <p>It may be useful to specify that the information contained in a stanza is valid only for a limited period of time. Such is the function of the "TTL" header, the value of which is some number of seconds since the creation of the stanza. Note well that this header is purely informational and MUST NOT be used for routing or delivery of XML stanzas, since that function is already served by &xep0079;. A stanza that includes the "TTL" header SHOULD also include a "Created" header so that the recipient can properly process the stanza.</p>
    <p>One situation in which both the "Created" and "TTL" headers might prove valuable is the broadcasting of structured presence information, such as a calendar-generated notification that a user will be in a meeting for the next hour:</p>
    <example caption='Time to Live for Presence Information'><![CDATA[
<presence>
  <show>dnd</show>
  <status>in a meeting</status>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Created'>2004-05-10T11:00Z</header>
    <header name='TTL'>3600</header>
  </headers>
</presence>
]]></example>
    <p>Another potential application is specifying a time to live for <cite>Service Discovery</cite> results, which helps other entities know how long to cache such information:</p>
    <example caption='Time to Live for Disco Information'><![CDATA[
<iq from='example.com'
    id='some-id'
    to='example.org'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='http://jabber.org/protocol/amp'/>
    ...
    <headers xmlns='http://jabber.org/protocol/shim'>
      <header name='Created'>2004-05-17T20:47Z</header>
      <header name='TTL'>86400</header>
    </headers>
  </query>
</iq>
]]></example>
  </section2>
  <section2 topic='Urgency' anchor='headers-urgency'>
    <p>It can be useful to specify that the information contained in a stanza is more or less time-sensitive (e.g., in order to help the recipient determine whether to attend to the information immediately or to delay attending to the information). Such is the function of the "Urgency" header, the value of which is "high", "medium", or "low". One use of the header is Sieve notifications (see &sievenotify;) sent via XMPP, as specified in &sievenotifyxmpp;.</p>
    <example caption='An Urgent Message'><![CDATA[
<message
    from='romeo@shakespeare.lit/orchard'
    to='juliet@capulet.com'
    type='chat'>
  <body>Wherefore are thou?!?</body>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='Urgency'>high</header>
  </headers>
</message>
]]></example>
  </section2>
</section1>
<section1 topic='A Note About Date-Related Headers' anchor='dates'>
  <p>Date formats differ widely. &xep0082; defines the Date, DateTime, and Time profiles of &iso8601;, which correspond to the Date, DateTime, and Time headers registered herein. The SHIM Date header also corresponds to the Date metadata element used in &DUBLINCORE; as specified in &rfc2413;.</p>
  <p>However, many Internet standards use a different datetime format that ultimately derives from &rfc0822; as updated by &rfc1123;; specifically, that format is used by email (&rfc2822;), the World Wide Web (<cite>RFC 2616</cite>), and the Session Initiation Protocol (<cite>RFC 3261</cite>). To map dates to and from these protocols, we define the SHIM RFC2822Date header.</p>
</section1>
<section1 topic='Security Considerations' anchor='security'>
  <p>In general, security considerations are the responsibility of the "using protocol".</p>
  <p>Certain SHIM headers MAY be security-sensitive (e.g., the "Classification", "Distribute", and "Store" headers specified herein). If an entity plans to use such headers, it MUST determine whether the intended recipient supports both the SHIM protocol and the particular security-sensitive headers of interst, as described under <link url='#disco'>Service Discovery</link>; furthermore, an implementation MUST warn a human user (if any) before use if the security-sensitive headers of interest are not supported.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
  <p>This document requires no interaction with &IANA;.</p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
    <p>The XMPP Registrar includes 'http://jabber.org/protocol/shim' in its registry of protocol namespaces (see &SHIMHEADERS;).</p>
  </section2>
  <section2 topic='Well-Known Service Discovery Nodes' anchor='registrar-nodes'>
    <p>The XMPP Registrar includes 'http://jabber.org/protocol/shim' in its registry of well-known Service Discovery nodes.</p>
  </section2>
  <section2 topic='SHIM Headers Registry' anchor='registrar-shim'>
    <p>The XMPP Registrar maintains a registry of SHIM headers.</p>
    <section3 topic='Process' anchor='registrar-shim-process'>
      &REGPROCESS;
      <code><![CDATA[
<header>
  <name>the value of the 'name' attribute</name>
  <desc>a natural-language description of the header</desc>
  <doc>the document in which this header is specified</doc>
</header>
]]></code>
      <p>The registrant may register more than one header at a time, each contained in a separate &lt;header/&gt; element.</p>
    </section3>
    <section3 topic='Initial Registration' anchor='registrar-shim-init'>
      <code><![CDATA[
<header>
  <name>Accept</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Accept-Charset</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Accept-Encoding</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Accept-Language</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Accept-Ranges</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Age</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Alert-Info</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Allow</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Authentication-Info</name>
  <desc>see RFC 2617</desc>
  <doc>RFC 2617</doc>
</header>

<header>
  <name>Cache-Control</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Call-ID</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Call-Info</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Classification</name>
  <desc>a level within a classification scheme</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Comments</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Connection</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Contact</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Content-Description</name>
  <desc>see RFC 2045</desc>
  <doc>RFC 2045</doc>
</header>

<header>
  <name>Content-Disposition</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Content-Encoding</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Content-ID</name>
  <desc>see RFC 2045</desc>
  <doc>RFC 2045</doc>
</header>

<header>
  <name>Content-Language</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Content-Length</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Content-Location</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Content-MD5</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Content-Range</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Content-Transfer-Encoding</name>
  <desc>see RFC 2045</desc>
  <doc>RFC 2045</doc>
</header>

<header>
  <name>Content-Type</name>
  <desc>see RFC 2045 or RFC 2616</desc>
  <doc>RFC 2045 or RFC 2616</doc>
</header>

<header>
  <name>Contributor</name>
  <desc>an entity other than the primary Creator who helped to create a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Coverage</name>
  <desc>the spatial or temporal characteristics of a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Created</name>
  <desc>date and time of stanza creation in ISO 8601 format</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Creator</name>
  <desc>the person or organization responsible for creating the content of a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>CSeq</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Date</name>
  <desc>a string that conforms to the Date profile specified in XEP-0082</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>DateTime</name>
  <desc>a string that conforms to the DateTime profile specified in XEP-0082</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Description</name>
  <desc>a textual description of the content of a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Distribute</name>
  <desc>whether or not the stanza may be further distributed</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Error-Info</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>ETag</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Expect</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Expires</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Format</name>
  <desc>the data format of a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Host</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Identifier</name>
  <desc>a string or number used to identity a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>If-Match</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>If-Modified-Since</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>If-None-Match</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>If-Range</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>If-Unmodified-Since</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>In-Reply-To</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Keywords</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Language</name>
  <desc>the language in expressing the content of a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Last-Modified</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Location</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Max-Forwards</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Message-ID</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>MIME-Version</name>
  <desc>see RFC 2045</desc>
  <doc>RFC 2045</doc>
</header>

<header>
  <name>Organization</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Pragma</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Priority</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Proxy-Authenticate</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Proxy-Authorization</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Publisher</name>
  <desc>the entity responsible for making a resource available</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Range</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Received</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Record-Route</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>References</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Referer</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Relation</name>
  <desc>the identifier of a second resource related to a primary resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Reply-To</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Require</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Resent-Bcc</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Resent-Cc</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Resent-Date</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Resent-From</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Resent-Message-Id</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Resent-Sender</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Resent-To</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Retry-After</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Return-Path</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>RFC2822Date</name>
  <desc>the datetime associated with an email message, SIP exchange, or HTTP request</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Rights</name>
  <desc>a rights management statement, identifier, or link</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Route</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Sender</name>
  <desc>see RFC 2822</desc>
  <doc>RFC 2822</doc>
</header>

<header>
  <name>Server</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Source</name>
  <desc>information about the original source of the present resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Store</name>
  <desc>whether or not the stanza may be stored or archived</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Subject</name>
  <desc>the human-readable topic of a message or resource</desc>
  <doc>RFC 2822 or RFC 2413</doc>
</header>

<header>
  <name>Supported</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>TE</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Time</name>
  <desc>a string that conforms to the Time profile specified in XEP-0082</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Timestamp</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Title</name>
  <desc>the name given to a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Trailer</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Transfer-Encoding</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>TTL</name>
  <desc>a time to live for the stanza, in seconds</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>Type</name>
  <desc>the category of a resource</desc>
  <doc>RFC 2413</doc>
</header>

<header>
  <name>Unsupported</name>
  <desc>see RFC 3261</desc>
  <doc>RFC 3261</doc>
</header>

<header>
  <name>Upgrade</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Urgency</name>
  <desc>the time sensitivity of a stanza ("high", "medium", or "low")</desc>
  <doc>XEP-0131</doc>
</header>

<header>
  <name>User-Agent</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Vary</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Via</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>Warning</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

<header>
  <name>WWW-Authenticate</name>
  <desc>see RFC 2616</desc>
  <doc>RFC 2616</doc>
</header>

]]></code>
    </section3>
  </section2>
</section1>
<section1 topic='XML Schema' anchor='schema'>
  <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://jabber.org/protocol/shim'
    xmlns='http://jabber.org/protocol/shim'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      XEP-0131: http://www.xmpp.org/extensions/xep-0131.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='headers'>
    <xs:complexType>
      <xs:sequence>
        <xs:element ref='header' minOccurs='0' maxOccurs='unbounded'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name='header'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:string'>
          <xs:attribute name='name' use='required'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

</xs:schema>
]]></code>
</section1>
</xep>