XEP-0481: Content Types in Messages

This specification describes a generic method whereby content in messages can be tagged as having a specific Internet Content Type. It also provides a method for sending the same content using different content types, as a fall-back mechanism when communicating between clients having different content type support.
Peter Waher
© 2016 – 2023 XMPP Standards Foundation. SEE LEGAL NOTICES.


WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.
Standards Track
0.1.0 (2023-05-04)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Stable
  4. Final

1. Introduction

Sometimes it is desirable for clients to communicate, or to send messages between each other, using a well defined Internet Content Type. Reasons can vary between the purely esthetic to funcional data-exchange. While there are XEPs, such as XHTML-IM (XEP-0071) [1] that provides means for sending richer content using a specific type, this extensions provides a similar mechanism, but for the general case of any content having a defined Internet Content Type.

Note: While the examples in this extensions uses Markdown as an example, any other text-based content type can be used.

2. Use Cases

2.1 Content type hint

The simplest use case is hinting at the content type of the textual content presented in the message body. This is done by aggregating a content element of namespace urn:xmpp:content to the message, with the attribute type specifying the content type. If the element does not provide a value, it is understood that the body contains the textual body of the content. This method should only be used if there's no risk of misunderstanding the message if the content type is not understood by the receiver, and the textual representation is readable. Example:

Example 1. Hinting at a content type
       <body>**Note:** This message is very important.</body>
       <content type='text/markdown' xmlns='urn:xmpp:content'/>

2.2 Alternate encoding

If there is a risk of misunderstanding the message if it's content type is not recognized, or the presentation of the message is done in an undesireable fashion, you can provide an alternate encoding of the message in the content element itself. If the content element contains a message, and the content type is recognized, the message should be taken from the content element instead of the body element. The body element in turn, should contain the plain text version of the same message. Example:

Example 2. Alternate encoding
       <body>Note: Go to Google and search for it.</body>
       <content type='text/markdown' xmlns='urn:xmpp:content'>
          **Note:** Go to [Google](http://www.google.com/) and search for it.

2.3 Alternate encodings

By providing multiple content elements in the same message, you can allow the receiver to choose the encoding best suited for its purpose. It also makes it possible to interchange messages that are understood by both humans and machines in the same message. If an empty content element is found, it is interpreted as above, i.e. providing a hint as to the content type of the message in the body element. Example:

Example 3. Alternate encodings
          Your energy consumption this month is 5000 kWh.
          That is very much. It will cost you 200 USD.
          You can find current tariffs at our web page.
       <content type='text/markdown' xmlns='urn:xmpp:content'>
          Your energy consumption this month is **5000 kWh**.
          That is *very much*. It will cost you **200 USD**.
          You can find current tariffs at our [web page](http://www.example.com/Energy).
       <content type='text/xml' xmlns='urn:xmpp:content'>
          &lt;Quote xmlns='somenamespace'&gt;
             &lt;Consumption unit='kWh'&gt5000&lt;/Consumption&gt;
             &lt;Cost unit='USD'&gt200&lt;/Cost&gt;

3. Determining Support

If an entity supports content types as specified herein, it MUST advertise that fact by returning a feature of "urn:xmpp:content" in response to Service Discovery (XEP-0030) [2] information requests.

Example 4. Service discovery information request
    <iq type='get'
      <query xmlns='http://jabber.org/protocol/disco#info'/>
Example 5. Service discovery information response
    <iq type='result'
      <query xmlns='http://jabber.org/protocol/disco#info'>
        <feature var='urn:xmpp:content'/>

In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities (XEP-0115) [3]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

4. Implementation Notes

4.1 Content Types

This document does not specify how content types are to be interpreted, or if content types are valid or well defined. It does not specify which content types are to be understood, or when. It only provides a means to hint or include different encodings in the same message.

4.2 Custom Content Types

It is possible to use custom or vendor-specific content types. These types are marked by prefixing the subtype with x. for custom unregistered types, and with vnd. for registered vendor specific types.

4.3 Stanza size

Care has to be taken when sending multiple encodings of the same message, as to not reach the smallest allowed maximum stanza size used by client and server software.

5. IANA Considerations

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

6. XMPP Registrar Considerations

The protocol schema needs to be added to the list of XMPP protocol schemas.

7. XML Schema

<?xml version='1.0' encoding='UTF-8'?>
© XMPP Standards Foundation, 2016
Author: Peter Waher

    <xs:element name='content'>
        <xs:complexType mixed='true'>
            <xs:attribute name='type' use='required'/>




Appendix A: Document Information

XMPP Standards Foundation
Standards Track
Last Updated
Approving Body
XMPP Council
XMPP Core, XEP-0030
Superseded By
Short Name
Source Control

This document in other formats: XML  PDF

Appendix B: Author Information

Peter Waher


This XMPP Extension Protocol is copyright © 1999 – 2024 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.

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).

Visual Presentation

The HTML representation (you are looking at) is maintained by the XSF. It is based on the YAML CSS Framework, which is licensed under the terms of the CC-BY-SA 2.0 license.

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 <https://xmpp.org/community/> 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. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

3. XEP-0115: Entity Capabilities <https://xmpp.org/extensions/xep-0115.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 https://xmpp.org/extensions/attic/

  1. Version 0.1.0 (2023-05-04)

    Promoting to Experimental.

    XEP Editor: ks
  2. Version 0.0.1 (2016-01-15)

    First draft.


Appendix I: Bib(La)TeX Entry

  title = {Content Types in Messages},
  author = {Waher, Peter},
  type = {XEP},
  number = {0481},
  version = {0.1.0},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0481.html},
  date = {2016-01-15/2023-05-04},