This document defines methods for exchanging instant messages that contain lightweight text markup. In the context of this document, "lightweight text markup" is to be understood as a combination of minimal structural elements and presentational styles that can easily be rendered on a wide variety of devices without requiring a full rich-text rendering engine such as a web browser. Examples of lightweight text markup include basic text blocks (e.g., paragraphs and blockquotes), structural elements (e.g., emphasis and strength), lists, hyperlinks, image references, and font styles (e.g., sizes and colors).
Note: This specification essentially defines a recommended set of XHTML elements and attributes for use in instant messaging by applying a series of "filters" to the wealth of XHTML features; however, developers of Jabber/XMPP clients mainly need to pay attention to the Summary of Recommendations rather than the complexities of how the recommendations are derived.
In the past, there have existed several incompatible methods within the Jabber community for exchanging instant messages that contain lightweight text markup. The most notable such methods have included derivatives of XHTML 1.0  as well as of Rich Text Format (RTF) .
Although it is sometimes easier for client developers to implement RTF support (this is especially true on certain Microsoft Windows operating systems), there are several reasons (consistent with the XMPP Design Guidelines (XEP-0134) ) for the XMPP Standards Foundation (XSF)  to avoid the use of RTF in developing a protocol for lightweight text markup. Specifically:
Conversely, there are several reasons to prefer XHTML for lightweight text markup:
Therefore, this document defines support for lightweight text markup in the form of an XMPP extension that encapsulates content defined by an XHTML 1.0 Integration Set that we label "XHTML-IM". The remainder of this document discusses lightweight text markup in terms of XHTML 1.0 only and does not further consider RTF or other technologies.
HTML was originally designed for authoring and presenting stuctured documents on the World Wide Web, and was subsequently extended to handle more advanced functionality such as image maps and interactive forms. However, the requirements for publishing documents (or developing transactional websites) for presentation by dedicated XHTML user agents on traditional computers or small-screen devices are fundamentally different from the requirements for lightweight text markup of instant messages; for this reason, only a reduced set of XHTML features is needed for XHTML-IM. In particular:
IM clients are not XHTML clients: their primary purpose is not to read pre-existing XHTML documents, but to read and generate relatively large numbers of fairly small instant messages.
The underlying context for XHTML content in Jabber/XMPP instant messaging is provided not by a full XHTML document, but by an XML stream, and specifically by a message stanza within that stream. Thus the <head/> element and all its children are unnecessary. Only the <body/> element and some of its children are appropriate for use in instant messaging.
The XHTML content that is read by one's IM client is normally generated on the fly by one's conversation partner (or, to be precise, by his or her IM client). Thus there is an inherent limit to the sophistication of the XHTML markup involved. Even in normal XHTML documents, fairly basic structural and rendering elements such as definition lists, abbreviations, addresses, and computer input handling (e.g., <kbd/> and <var/>) are relatively rare. There is little or no foreseeable need for such elements within the context of instant messaging.
The foregoing is doubly true of more advanced markup such as tables, frames, and forms (however, there exists an XMPP extension that provides an instant messaging equivalent of the latter, as defined in Data Forms (XEP-0004) ).
Although ad-hoc styles are useful for messaging (by means of the 'style' attribute), full support for Cascading Style Sheets  (defined by the <style/> element or a standalone .css file, and implemented via the 'class' attribute) would be overkill since many CSS1 properties (e.g., box, classification, and text properties) were developed especially for sophisticated page layout.
Background images, audio, animated text, layers, applets, scripts, and other multimedia content types are unnecessary, especially given the existence of XMPP extensions such as SI File Transfer (XEP-0096) , Jingle (XEP-0166) , and Jingle File Transfer (XEP-0234) .
Content transformations such as those defined by XSL Transformations  must not be necessary in order for an instant messaging application to present lightweight text markup to an end user.
As explained below, some of these requirements are addressed by the definition of the XHTML-IM Integration Set itself, while others are addressed by a recommended "profile" for that Integration Set in the context of instant messaging applications.
This document defines an adaptation of XHTML 1.0 (specifically, an XHTML 1.0 Integration Set) that makes it possible to provide lightweight text markup of instant messages (mainly for Jabber/XMPP instant messages, although the Integration Set defined herein could be used by other protocols). This pattern is familiar from email, wherein the HTML-formatted version of the message supplements but does not supersede the text-only version of the message. 
In Jabber/XMPP communications, the meaning (as opposed to markup) of the message MUST always be represented as best as possible in the normal <body/> child element or elements of the <message/> stanza qualified by the 'jabber:client' (or 'jabber:server') namespace. Lightweight text markup is then provided within an <html/> element qualified by the 'http://jabber.org/protocol/xhtml-im' namespace.  However, this <html/> element is used solely as a "wrapper" for the XHTML content itself, which content is encapsulated via one or more <body/> elements qualified by the 'http://www.w3.org/1999/xhtml' namespace, along with appropriate child elements thereof.
The following example illustrates this approach.
Technically speaking, there are three aspects to the approach taken herein:
These three aspects are defined in the three document sections that follow.
The root element for including XHTML content within XMPP stanzas is <html/>. This element is qualified by the 'http://jabber.org/protocol/xhtml-im' namespace. From the perspective of XMPP, the wrapper element functions as an XMPP extension element; from the perspective of XHTML, it functions as a wrapper for XHTML 1.0 content qualified by the 'http://www.w3.org/1999/xhtml' namespace. Such XHTML content MUST be contained in one or more <body/> elements qualified by the 'http://www.w3.org/1999/xhtml' namespace and MUST conform to the XHTML-IM Integration Set defined in the following section. If more than one <body/> element is included in the <html/> wrapper element, each <body/> element MUST possess an 'xml:lang' attribute with a distinct value, where the value of that attribute MUST adhere to the rules defined in RFC 5646 . A formal definition of the <html/> element is provided in the XHTML-IM Wrapper Schema.
The XHTML <body/> element is not to be confused with the XMPP <body/> element, which is a child of a <message/> stanza and is qualified by the 'jabber:client' or 'jabber:server' namespace as described in XMPP IM . The <html/> wrapper element is intended for inclusion only as a direct child element of the XMPP <message/> stanza and only in order to specify a marked-up version of the message <body/> element or elements, but MAY be included elsewhere in accordance with the "extended namespace" rules defined in the XMPP IM specification.
Until and unless (1) additional integration sets are defined and (2) mechanisms are specified for discovering or negotiating which integration sets are supported, the XHTML markup contained within the <html/> wrapper element:
Note: In the foregoing restrictions, the meaning of "ignore" is defined by the conformance requirements of Modularization of XHTML, as summarized in the User Agent Conformance section of this document).
This section defines an XHTML 1.0 Integration Set for use in the context of instant messaging. Given its intended usage, we label it "XHTML-IM".
Modularization of XHTML provides the ability to formally define subsets of XHTML 1.0 via the concept of "modularization" (which may be familiar from XHTML Basic ). Many of the defined modules are not necessary or useful in the context of instant messaging, and in the context of Jabber/XMPP instant messaging specifically some modules have been superseded by well-defined XMPP extensions. This document specifies that XHTML-IM shall be based on the following XHTML 1.0 modules:
Modularization of XHTML defines many additional modules, such as Table Modules, Form Modules, Object Modules, and Frame Modules. None of these modules is part of the XHTML-IM Integration Set. If support for such modules is desired, it MUST be defined in a separate and distinct integration set.
The Structure Module is defined as including the following elements and attributes: 
|<body/>||class, id, title; style|
The Text Module is defined as including the following elements and attributes:
|<abbr/>||class, id, title; style|
|<acronym/>||class, id, title; style|
|<address/>||class, id, title; style|
|<blockquote/>||class, id, title; style; cite|
|<br/>||class, id, title; style|
|<cite/>||class, id, title; style|
|<code/>||class, id, title; style|
|<dfn/>||class, id, title; style|
|<div/>||class, id, title; style|
|<em/>||class, id, title; style|
|<h1/>||class, id, title; style|
|<h2/>||class, id, title; style|
|<h3/>||class, id, title; style|
|<h4/>||class, id, title; style|
|<h5/>||class, id, title; style|
|<h6/>||class, id, title; style|
|<kbd/>||class, id, title; style|
|<p/>||class, id, title; style|
|<pre/>||class, id, title; style|
|<q/>||class, id, title; style; cite|
|<samp/>||class, id, title; style|
|<span/>||class, id, title; style|
|<strong/>||class, id, title; style|
|<var/>||class, id, title; style|
The Hypertext Module is defined as including the <a/> element only:
|<a/>||class, id, title; style; accesskey, charset, href, hreflang, rel, rev, tabindex, type|
The List Module is defined as including the following elements and attributes:
|<dl/>||class, id, title; style|
|<dt/>||class, id, title; style|
|<dd/>||class, id, title; style|
|<ol/>||class, id, title; style|
|<ul/>||class, id, title; style|
|<li/>||class, id, title; style|
The Image Module is defined as including the <img/> element only:
|<img/>||class, id, title; style; alt, height, longdesc, src, width|
The Style Attribute Module is defined as including the style attribute only, as included in the preceding definition tables.
Even within the restricted set of modules specified as defining the XHTML-IM Integration Set (see preceding section), some elements and attributes are inappropriate or unnecessary for the purpose of instant messaging; although such elements and attributes MAY be included in accordance with the XHTML-IM Integration Set, further recommended restrictions regarding which elements and attributes to include in XHTML content are specified below.
The intent of the protocol defined herein is to support lightweight text markup of XMPP message bodies only. Therefore the <head/>, <html/>, and <title/> elements SHOULD NOT be generated by a compliant implementation, and SHOULD be ignored if received (where the meaning of "ignore" is defined by the conformance requirements of Modularization of XHTML, as summarized in the User Agent Conformance section of this document). However, the <body/> element is REQUIRED, since it is the root element for all XHTML-IM content.
Not all of the Text Module elements are appropriate in the context of instant messaging, since the XHTML content that one views is generated by one's conversation partner in what is often a rapid-fire conversation thread. Only the following elements are RECOMMENDED in XHTML-IM:
The other Text Module elements MAY be generated by a compliant implementation but MAY be ignored if received (where the meaning of "ignore" is defined by the conformance requirements of Modularization of XHTML, as summarized in the User Agent Conformance section of this document).
The only recommended attributes of the <a/> element are specified in the Recommended Attributes section of this document.
Because it is unlikely that an instant messaging user would generate a definition list, only ordered and unordered lists are RECOMMENDED. Definition lists SHOULD NOT be generated by a compliant implementation, and SHOULD be ignored if received (where the meaning of "ignore" is defined by the conformance requirements of Modularization of XHTML, as summarized in the User Agent Conformance section of this document).
The only recommended attributes of the <img/> element are specified in the Recommended Attributes section of this document.
The XHTML specification allows a "data:" URL RFC 2397  as the value of the 'src' attribute. This is NOT RECOMMENDED for use in XHTML-IM, because it can significantly increase the size of the message stanza and XMPP is not optimized for large stanzas. If the image data is small (less than 8 kilobytes), clients MAY use Bits of Binary (XEP-0231)  in coordination with XHTML-IM; if the image data is large, the value of the 'src' SHOULD be a pointer to an externally available file for the image (or the sender SHOULD use a dedicated file transfer method such as In-Band Bytestreams (XEP-0047)  or SOCKS5 Bytestreams (XEP-0065) ).
For security reasons or because of display constraints, a compliant client MAY choose to display 'alt' text only, not the image itself (for details, see the Malicious Objects section of this document).
This module MUST be supported in XHTML-IM if possible; although clients written for certain platforms (e.g., console clients, mobile phones, and handheld computers) or for certain classes of users (e.g., text-to-speech clients) might not be able to support all of the recommended styles directly, they SHOULD attempt to emulate or translate the defined style properties into text or other presentation styles that are appropriate for the platform or user base in question.
A full list of recommended style properties is provided below.
CSS1 defines 42 "atomic" style properties (which are categorized into font, color and background, text, box, and classification properties) as well as 11 "shorthand" properties ("font", "background", "margin", "padding", "border-width", "border-top", "border-right", "border-bottom", "border-left", "border", and "list-style"). Many of these properties are not appropriate for use in text-based instant messaging, for one or more of the following reasons:
Unfortunately, CSS1 does not include mechanisms for defining profiles thereof (as does XHTML 1.0 in the form of XHTML Modularization). While there exist reduced sets of CSS2, these introduce more complexity than is desirable in the context of XHTML-IM. Therefore we simply provide a list of recommended CSS1 style properties.
XHTML-IM stipulates that only the following style properties are RECOMMENDED:
Although a compliant implementation MAY generate or process other style properties defined in CSS1, such behavior is NOT RECOMMENDED by this document.
Section 5.1 of Modularization of XHTML describes several "common" attribute collections: a "Core" collection ('class', 'id', 'title'), an "I18N" collection ('xml:lang', not shown below since it is implied in XML), an "Events" collection (not included in the XHTML-IM Integration Set because the Intrinsic Events Module is not selected), and a "Style" collection ('style'). The following table summarizes the recommended profile of these common attributes within the XHTML 1.0 content itself:
|class||NOT RECOMMENDED||External stylesheets (which 'class' would typically reference) are not recommended.|
|id||NOT RECOMMENDED||Internal links and message fragments are not recommended in IM content, nor are external stylesheets (which also make use of the 'id' attribute).|
|title||NOT RECOMMENDED||Granting of titles to elements in IM content seems unnecessary.|
|style||REQUIRED||The 'style' attribute is required since it is the vehicle for presentational styles.|
|xml:lang||NOT RECOMMENDED||Differentiation of language identification SHOULD occur at the level of the <body/> element only.|
Beyond the "common" attributes, certain elements within the modules selected for the XHTML-IM Integration Set are allowed to possess other attributes, such as eight attributes for the <a/> element and five attributes for the <img/> element. The recommended profile for such attributes is provided in the following table:
Other XHTML 1.0 attributes SHOULD NOT be generated by a compliant implementation, and SHOULD be ignored if received (where the meaning of "ignore" is defined by the conformance requirements of Modularization of XHTML, as summarized in the User Agent Conformance section of this document).
The following table summarizes the elements and attributes that are recommended within the XHTML-IM Integration Set.
|<a/>||href, style, type|
|<body/>||style, xml:lang |
|<img/>||alt, height, src, style, width|
Any other elements and attributes defined in the XHTML 1.0 modules that are included in the XHTML-IM Integration Set SHOULD NOT be generated by a compliant implementation, and SHOULD be ignored if received (where the meaning of "ignore" is defined by the conformance requirements of Modularization of XHTML, as summarized in the User Agent Conformance section of this document).
The following rules apply to the generation and processing of XHTML content by Jabber clients or other XMPP entities.
XHTML-IM content is designed to provide a formatted version of the XML character data provided in the <body/> of an XMPP <message/> stanza; if such content is included in an XMPP message, the <html/> element MUST be a direct child of the <message/> stanza and the XHTML-IM content MUST be understood as a formatted version of the message body. XHTML-IM content MAY be included within XMPP <iq/> stanzas (or children thereof), but any such usage is undefined. In order to preserve bandwidth, XHTML-IM content SHOULD NOT be included within XMPP <presence/> stanzas; however, if it is so included, the <html/> element MUST be a direct child of the <presence/> stanza and the XHTML-IM content MUST be understood as a formatted version of the XML character data provided in the <status/> element.
The sending client MUST ensure that, if XHTML content is sent, its meaning is the same as that of the plaintext version, and that the two versions differ only in markup rather than meaning.
XHTML-IM is a reduced set of XHTML 1.0 and thus also of XML 1.0. Therefore all opening tags MUST be completed by inclusion of an appropriate closing tag.
XMPP Core specifies that an XMPP <message/> MAY contain more than one <body/> child as long as each <body/> possesses an 'xml:lang' attribute with a distinct value. In order to ensure correct internationalization, if an XMPP <message/> stanza contains more than one <body/> child and is also sent as XHTML-IM, the <html/> element SHOULD also contain more than one <body/> child, with one such element for each <body/> child of the <message/> stanza (distinguished by an appropriate 'xml:lang' attribute).
Section 11.1 of XMPP Core stipulates that character entities other than the five general entities defined in Section 4.6 of the XML specification (i.e., <, >, &, ', and ") MUST NOT be sent over an XML stream. Therefore implementations of XHTML-IM MUST NOT include predefined XHTML 1.0 entities such as -- instead, implementations MUST use the equivalent character references as specified in Section 4.1 of the XML specification (even in non-obvious places such as URIs that are included in the 'href' attribute).
For elements and attributes qualified by the 'http://www.w3.org/1999/xhtml' namespace, user agent conformance is guided by the requirements defined in Modularization of XHTML; for details, refer to the User Agent Conformance section of this document.
Where strictly presentational style are desired (e.g., colored text), it might be necessary to use 'style' attributes (e.g., <span style='font-color: green'>this is green</span>). However, where possible it is instead RECOMMENDED to use appropriate structural elements (e.g., <strong/> and <blockquote/> instead of, say, style='font-weight: bold' or style='margin-left: 5%').
Nesting of block structural elements (<p/>) and list elements (<dl/>, <ol/>, <ul/>) is NOT RECOMMENDED, except within <div/> elements.
It is RECOMMENDED for implementations to replace line breaks with the <br/> element and to replace significant whitepace with the appropriate number of non-breaking spaces (via the NO-BREAK SPACE character or its equivalent), where "significant whitespace" means whitespace that makes some material difference (e.g., one or more spaces at the beginning of a line or more than one space anywhere else within a line), not "normal" whitespace separating words or punctuation.
When rendering XHTML-IM content, a receiving user agent MUST NOT render as XHTML any text that was not structured by the sending user agent using XHTML elements and attributes; if the sender wishes text to be structured (e.g., for certain words to be emphasized or for URIs to be linked), the sending user agent MUST represent the text using the appropriate XHTML elements and attributes.
The following examples provide an insight into the inclusion of XHTML content in XMPP <message/> stanzas but are by no means exhaustive or definitive.
(Note: The examples might not render correctly in all web browsers, since not all web browsers comply fully with the XHTML 1.0 and CSS1 standards. Markup in the examples may include line breaks for readability. Example renderings are shown with a colored background to set them off from the rest of the text.)
This could be rendered as follows:
This could be rendered as follows:
This could be rendered as follows:
Hey, are you licensed to Jabber?
Note the large size of the image. Including the 'height' and 'width' attributes is therefore quite friendly, since it gives the receiving application hints as to whether the image is too large to fit into the current interface (naturally, these are hints only and cannot necessarily be relied upon in determining the size of the image).
Rendering the 'alt' value rather than the image would yield something like the following:
This could be rendered as follows:
Although quoting received messages is relatively uncommon in IM, it does happen. This could be rendered as follows:
How multiple bodies would best be rendered will depend on the user agent and relevant application. For example, a specialized Jabber client that is used in foreign language instruction might show two languages side by side, whereas a dedicated IM client might show content only in a human user's preferred language as captured in the client configuration.
Let us assume that the recipient's user agent recognizes neither the <acronym/> element (which is discouraged in XHTML-IM) nor the 'type' and 'start' attributes of the <ol/> element (which, after all, were deprecated in HTML 4.0), and that it does not render nested elements (e.g., the <p/> elements within the <li/> elements); in this case, it could render the content as follows (note that the element value is shown as text and the attribute value is not rendered):
This section describes methods for discovering whether a Jabber client or other XMPP entity supports the protocol defined herein.
If the queried entity supports XHTML-IM, it MUST return a <feature/> element with a 'var' attribute set to a value of "http://jabber.org/protocol/xhtml-im" in the IQ result.
A Jabber user's client MAY send XML <message/> stanzas containing XHTML-IM extensions without first discovering if the conversation partner's client supports XHTML-IM. If the user's client sends a message that includes XHTML-IM markup and the conversation partner's client replies to that message but does not include XHTML-IM markup, the user's client SHOULD NOT continue sending XHTML-IM markup.
While scripts, applets, binary objects and other potentially executable code is excluded from the profiles used in XHTML-IM, malicious entities still may inject those and thus exploit entities which rely on this exclusion. Entities thus MUST assume that inbound XHTML-IM may be mailicious and MUST sanitize it according to the profile used, by ignoring elements and removing attributes as needed.
To further reduce the risk of such exposure, an implementation MAY choose to:
In addition, an implementation MUST make it possible for a user to prevent the automatic fetching and presentation of images (rather than leave it up to the implementation).
To reduce the risk of phishing attacks , an implementation MAY choose to:
The network availability of the receiver may be revealed if the receiver's client automatically loads images or the receiver clicks a link included in a message. Therefore an implementation MAY choose to:
The usage of XHTML 1.0 defined herein meets the requirements for XHTML 1.0 Integration Set document type conformance as defined in Section 3 ("Conformance Definition") of Modularization of XHTML.
The Formal Public Identifier (FPI) for the XHTML-IM document type definition is:
The fields of this FPI are as follows:
A user agent that implements this specification MUST conform to Section 3.5 ("XHTML Family User Agent Conformance") of Modularization of XHTML. Many of the requirements defined therein are already met by Jabber clients simply because they already include XML parsers.
However, "ignore" has a special meaning in XHTML modularization (different from its meaning in XMPP). Specifically, criteria 4 through 6 of Section 3.5 of Modularization of XHTML state:
W3C TEXT: If a user agent encounters an element it does not recognize, it must continue to process the children of that element. If the content is text, the text must be presented to the user.
XSF COMMENT: This behavior is different from that defined by XMPP Core, and in the context of XHTML-IM implementations applies only to XML elements qualified by the 'http://www.w3.org/1999/xhtml' namespace as defined herein. This criterion MUST be applied to all XHTML 1.0 elements except those explicitly included in XHTML-IM as described in the XHTML-IM Integration Set and Recommended Profile sections of this document. Therefore, an XHTML-IM implementation MUST process all XHTML 1.0 child elements of the XHTML-IM <html/> element even if such child elements are not included in the XHTML 1.0 Integration Set defined herein, and MUST present to the recipient the XML character data contained in such child elements.
W3C TEXT: If a user agent encounters an attribute it does not recognize, it must ignore the entire attribute specification (i.e., the attribute and its value).
XSF COMMENT: This criterion MUST be applied to all XHTML 1.0 attributes except those explicitly included in XHTML-IM as described in the XHTML-IM Integration Set and Recommended Profile sections of this document. Therefore, an XHTML-IM implementation MUST ignore all attributes of elements qualified by the 'http://www.w3.org/1999/xhtml' namespace if such attributes are not explicitly included in the XHTML 1.0 Integration Set defined herein.
W3C TEXT: If a user agent encounters an attribute value it doesn't recognize, it must use the default attribute value.
XSF COMMENT: Since not one of the attributes included in XHTML-IM has a default value defined for it in XHTML 1.0, in practice this criterion does not apply to XHTML-IM implementations.
For information regarding XHTML modularization in XML schema for the XHTML 1.0 Integration Set defined in this specification, refer to the Schema Driver section of this document.
The XHTML 1.0 Integration Set defined herein has been reviewed informally by an editor of the XHTML Modularization in XML Schema specification but has not undergone formal review by the W3C. Before the XHTML-IM specification proceeds to a status of Final within the standards process of the XMPP Standards Foundation, the XMPP Council  is encouraged to pursue a formal review through communication with the Hypertext Coordination Group within the W3C.
The W3C is actively working on XHTML 2.0  and may produce additional versions of XHTML in the future. This specification addresses XHTML 1.0 only, but it may be superseded or supplemented in the future by a XMPP Extension Protocol specification that defines methods for encapsulating XHTML 2.0 content in XMPP.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
The following schema defines the XMPP extension element that serves as a wrapper for XHTML content.
The following schema defines the modularization schema driver for XHTML-IM.
The following schema defines the content model for XHTML-IM.
This specification formalizes and extends earlier work by Jeremie Miller and Julian Missig on XHTML formatting of Jabber messages. Many thanks to Shane McCarron for his assistance regarding XHTML modularization and conformance issues. Thanks also to contributors on the discussion list of the XSF's Standards SIG  for their feedback and suggestions.
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This XMPP Extension Protocol is copyright © 1999 – 2018 by the XMPP Standards Foundation (XSF).
Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.
## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##
In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.
This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).
The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <firstname.lastname@example.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <email@example.com>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
2. Rich Text Format (RTF) Version 1.5 Specification <http://msdn.microsoft.com/library/en-us/dnrtfspec/html/rtfspec.asp>.
4. The XMPP Standards Foundation (XSF) is an independent, non-profit membership organization that develops open extensions to the IETF's Extensible Messaging and Presence Protocol (XMPP). For further information, see <https://xmpp.org/about/xmpp-standards-foundation>.
15. The XHTML is merely an alternative version of the message body or bodies, and the semantic meaning is to be derived from the textual message body or bodies rather than the XHTML version.
16. It might have been better to use an element name other than <html/> for the wrapper element; however, changing it would not be backwards-compatible with the older protocol and existing implementations.
17. Modularization of XHTML <http://www.w3.org/TR/2004/WD-xhtml-modularization-20040218/>.
21. The 'style' attribute is specified herein where appropriate because the Style Attribute Module is included in the definition of the XHTML-IM Integration Set, whereas the event-related attributes (e.g., 'onclick') are not specified because the Implicit Events Module is not included.
26. When contained within the <html xmlns='http://jabber.org/protocol/xhtml-im'> element, a <body/> element is qualified by the 'http://www.w3.org/1999/xhtml' namespace; naturally, this is a namespace declaration rather than an attribute per se, and therefore is not mentioned in the attribute enumeration.
29. Phishing has been defined by the Financial Services Technology Consortium Counter-Phishing Initiative as "a broadly launched social engineering attack in which an electronic identity is misrepresented in an attempt to trick individuals into revealing personal credentials that can be used fraudulently against them".
30. The XMPP Council is a technical steering committee, authorized by the XSF Board of Directors and elected by XSF members, that approves of new XMPP Extensions Protocols and oversees the XSF's standards process. For further information, see <https://xmpp.org/about/xmpp-standards-foundation#council>.
32. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
33. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
34. The Standards SIG is a standing Special Interest Group devoted to development of XMPP Extension Protocols. The discussion list of the Standards SIG is the primary venue for discussion of XMPP protocol extensions, as well as for announcements by the XMPP Extensions Editor and XMPP Registrar. To subscribe to the list or view the list archives, visit <https://mail.jabber.org/mailman/listinfo/standards/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Correction: Council voted to Deprecate, not Obsolete.
Per a vote of the XMPP Council, advanced to Obsolete.
Clarify security considerations.
Update plain version of blockquote example to escape <div/> (Thijs Alkemade).
Addressed feedback received during Call for Experience: (1) generalized business rule about not adding XHTML rendering in the receiving client, (2) modified business rule about structure vs. style to recommend structural elements.
Encouraged support for several more structural elements from the text module (blockquote, cite, em, and strong); further clarified security considerations regarding fetching and presentation of images; modified several examples; clarified several points throughout the text.
Reorganized and further clarified security considerations regarding malicious objects, phishing, and presence leaks; added business rule about inclusion and processing of hyperlinks.
Clarified security considerations regarding images.
More clearly specified that XHTML-IM content is intended for use only within message stanzas, that it may be included in IQ stanzas (usage undefined) and that it may be included in presence stanzas (usage: formatted version of status); specified security consideration regarding hyperlinks.
Per a vote of the Jabber Council, advanced status to Draft.
Per list discussion, removed recommendation to preserve whitespace in XHTML bodies (instead, use of <br/> and non-breaking spaces is recommended); noted that nesting of elements is not recommended except within <div/> elements; and switched from padding-left to margin-left for indentation.
Added recommendation to preserve whitespace in XHTML bodies.
Simplified the recommended profiles based on list discussion; changed the examples accordingly.
Specified the scope of the proposal; clarified reasons for the choice of technology; clarified one business rule; corrected several typographical errors.
Based on W3C feedback, added content model and refactored the text to ensure separation between the XHTML 1.0 Integration Set itself and the XSF's recommended profile of the Integration Set; also split the requirements out from the Concepts and Approach section, added several more examples, and showed renderings of the examples.
Clarified relationship between wrapper element and XHTML content.
Initial version of XHTML modularization.
Clarified and corrected several points in the text; improved and added to the examples.
Defined XHTML 1.0 Integration Set conformance; removed schema pending work on XHTML modularization with W3C.
Cleaned up the schema; added W3C considerations.
Changed status to Deferred pending discussion with the W3C regarding XHTML modularization.
Changed MUST to SHOULD for support of the Style Attribute Module; clarified relationship of XHTML-IM schema to XHTML schema; slight text cleanup.
Added the <code/> element.
Made image support recommended (not mandatory); removed references to conversation threads; fixed some issues in the schema; made small editorial changes throughout.
Fixed the schema, made several small editorial changes.
Brought back several content-based elements; added preliminary schema.
Defined the attributes and style properties required by this document.
Described the requirements more fully; added additional restrictions above and beyond the standard XHTML 1.0 Modules; added disco examples.