XEP-0394: Message Markup

Abstract:	This specification provides an alternative to XHTML-IM with rigid separation of content and markup information, improving the resilience against spoofing and injection attacks.
Author:	Konstzntin Kozlov
Copyright:	© 1999 – 2018 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:	Deferred
Type:	Standards Track
Version:	0.2.1
Last Updated:	2019-01-05

WARNING: This document has been automatically Deferred after 12 months of inactivity in its previous Experimental state. Implementation of the protocol described herein is not recommended for production systems. However, exploratory implementations are encouraged to resume the standards process.

1. Introduction
2. Requirements
3. Glossary
4. Use Cases
    4.1. Transport inline markup
    4.2. Transport code blocks
    4.3. Transport itemized lists
    4.4. Transport blockquotes
5. Business Rules
6. Implementation Notes
7. Accessibility Considerations
8. Internationalization Considerations
9. Security Considerations
10. IANA Considerations
11. XMPP Registrar Considerations
12. XML Schema
13. Acknowledgements

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

1. Introduction

Currently, XHTML-IM (XEP-0071) [1] or ad-hoc text-based formats are used to provide styling and semantic information in messages sent over the XMPP network.

These approaches have several drawbacks, including but not limited to:

Lack of standardisation (ad-hoc text-based formats), and thus interoperability.
Lack of extensibility (ad-hoc text-based formats).
Pollution of <body/> with markup information (ad-hoc text-based formats), possibly reducing accessiblity.
Possibility of sending different textual content in the marked-up version vs. the plain-text version (XHTML-IM), allowing for spoofing attacks.
Difficult to sanitize potentially malicious input (XHTML-IM mostly) (see e.g. Security Issues with XHTML-IM (again) [2]), leading to injection attacks.

2. Requirements

Textual data and markup metadata MUST be separated strictly.
There MUST only be a single source of truth for the text associated with each content language in a message.
The markup specification MUST be extensible in order to support more complex use-cases in the futurue.
The markup SHOULD convey semantic information, if possible, as opposed to stylistic information.
Entities SHOULD be able to cherry-pick a subset of the markup which is suitable for their presentation (for example, a terminal-based client may support inline emphasis and strike through, but no block-level markup).
The specification MUST NOT require server support.
Messages using this markup MUST NOT reduce readability for text-to-speech engines and other accessibility technologies.
Messages using this markup MUST NOT reduce readability for people with color vision deficiencies.
Requirements on the contents of the <body/> MUST NOT be imposed.

3. Glossary

OPTIONAL.

4. Use Cases

4.1 Transport inline markup

Inline markup is declared with the <span/> element.

Example 1.

<message>
  <body>There is really no reason to worry.</body>
  <markup xmlns="urn:xmpp:markup:0">
    <span start="9" end="15">
      <emphasis/>
    </span>
  </markup>
</message>

The following child elements are defined for <span/>:

<emphasis/>: The spanned range is emphasized. Suggested rendering: italics or bold.
<code/>: The spanned range is some kind of machine code. Suggested rendering: monospaced.
<deleted/>: The spanned range has been deleted. Suggested rendering: striked through.

The start and end attributes define the range at which the span is applied. They are in units of unicode code points in the character data if the body element. The first affected codepoint is the one at start (where the first codepoint of a message has index 0) and the last affected codepoint is the one just before end. The above example could render in HTML as:

There is really no reason to worry.

4.2 Transport code blocks

Code blocks are declared with the <bcode/> element:

Example 2.

<message>
  <body>Just run this command:
$ cowsay XMPP is awesome.</body>
  <markup xmlns="urn:xmpp:markup:0">
    <bcode start="23" end="48"/>
  </markup>
</message>

The start and end attributes work just like for <span/>.

The suggested rendering of code blocks is as block-level elements with monospaced font. The above example could render in HTML as:

Just run this command:

$ cowsay XMPP is awesome.

4.3 Transport itemized lists

Itemized lists are declared with the <list/> and <li/> elements:

Example 3.

<message>
  <body>This XEP supports many things:
* inline markup
* code blocks
* lists
* and possibly more!</body>
  <markup xmlns="urn:xmpp:markup:0">
    <list start="31" end="89">
      <li start="31"/>
      <li start="47"/>
      <li start="61"/>
      <li start="69"/>
    </list>
  </markup>
</message>

The start and end attributes of <list/> define the scope of the list. The start of the <li/> elements denote the start of a new list item. A list item continues until the end of the list or the start of the next list item. The first <li/> in a <list/> MUST have a start value equal to the start value of the <list/>.

The above example could render in HTML as:

This XEP supports many things:

* inline markup
* code blocks
* lists
* and possibly more!

4.4 Transport blockquotes

A block quote is declared with a <bquote/> element:

Example 4.

<message>
  <body>He said:
&gt; Thou shalt not pass!
and raised his hand.</body>
  <markup xmlns="urn:xmpp:markup:0">
    <bquote start="9" end="32"/>
  </markup>
</message>

In addition, References (XEP-0372) [3] or a similar mechanism MAY be used to attribute the origin of the quote. The above example could render in HTML as:

He said:

> Thou shalt not pass!

and raised his hand.

A nested quotation can be created by adding two <bquote/> elements where the start/end range is nested. If plain text quotation markers are used, the start of the blockquote MUST be placed at the first quotation marker of the outer quote.

Example 5.

<message>
  <body>&gt; He said:
&gt;&gt; Thou shalt not pass!
&gt; and raised his hand.

Isn't this from some famous movie?</body>
  <markup xmlns="urn:xmpp:markup:0">
    <bquote start="0" end="57"/>
    <bquote start="11" end="34"/>
  </markup>
</message>

The above example could render in HTML as:

> He said:
>> Thou shalt not pass!
> and raised his hand.

Isn't this from some famous movie?

5. Business Rules

Spans MUST NOT overlap with each other.
Spans MUST NOT overlap with the boundaries of a block-level markup element, but MAY be fully contained within a block-level markup element.
Block level markup elements MUST NOT overlap with each others boundaries.
There MUST NOT be a <markup/> element in a <message/> without corresponding <body/>. Note that there may be one <markup/> elements with appropriate xml:lang attribute value for each <body/>, if the message contains multiple <body/> elements.
The start and end attributes operate on unicode code points in the XML character data of the corresponding <body/> element.
Entities MUST silently ignore elements and attributes (arbitrarly deep) in <markup/> which they do not understand; this allows for future extensions of the markup without breaking existing implementations.

6. Implementation Notes

OPTIONAL.

7. Accessibility Considerations

Entities are encouraged use the semantic information to make the presentation of the textual content more precise, for example by applying spoken emphasis to passages marked with an <emphasis/> <span/>.

8. Internationalization Considerations

Since a message may have multiple <body/> elements in different languages, there MAY be multiple <markup/> elements, one for each of the <body/> elements. There is no requirement to include a <markup/> element for each language.

9. Security Considerations

REQUIRED.

10. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [4].

11. XMPP Registrar Considerations

This specification defines the following XML namespaces:

urn:xmpp:markup:0

12. XML Schema

REQUIRED for protocol specifications.

13. Acknowledgements

Thanks to Georg Lukas and Emmanuel Gil Peyrot for feedback on the initial idea of this XEP.

Appendices

Appendix A: Document Information

Series: XEP
Number: 0394
Publisher: XMPP Standards Foundation
Status: Deferred
Type: Standards Track
Version: 0.2.1
Last Updated: 2019-01-05
Approving Body: XMPP Council
Dependencies: None
Supersedes: None
Superseded By: None
Short Name: markup
Source Control: HTML
This document in other formats: XML PDF

Appendix B: Author Information

Konstzntin Kozlov

Email: yagiza@yandex.ru
JabberID: yagiza@isgeek.info

Appendix C: Legal Notices

Copyright

Permissions

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.

Disclaimer of Warranty

## 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. ##

Limitation of Liability

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.

IPR Conformance

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).

Appendix D: Relation to XMPP

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.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.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 <editor@xmpp.org>.

Appendix F: Requirements Conformance

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".

Appendix G: Notes

1. XEP-0071: XHTML-IM <https://xmpp.org/extensions/xep-0071.html>.

2. Security Issues with XHTML-IM (again) <https://mail.jabber.org/pipermail/standards/2017-October/033546.html>.

3. XEP-0372: References <https://xmpp.org/extensions/xep-0372.html>.

4. 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/>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.2.1 (2019-01-05)

Adopt deferred XEP. (kks)

Version 0.2.0 (2018-12-06)

Defer due to lack of activity. (XEP Editor (jsc))

Version 0.1.0 (2017-11-22)

First draft approved by the XMPP Council.

(XEP Editor (ssw))

Version 0.0.1 (2017-11-07)

First draft.

(jwi)

END