XEP-xxxx: Content Rating Labels

This specification provides a wire format in the form of a Service Discovery extension to allow services of various kinds to publish information about the kind of content they allow and/or endorse on their platform.
Jonas Schäfer
© 2021 – 2021 XMPP Standards Foundation. SEE LEGAL NOTICES.


WARNING: This document has not yet been accepted for consideration or approved in any official manner by the XMPP Standards Foundation, and this document is not yet an XMPP Extension Protocol (XEP). If this document is accepted as a XEP by the XMPP Council, it will be published at <https://xmpp.org/extensions/> and announced on the <standards@xmpp.org> mailing list.
Standards Track
0.0.1 (2021-03-03)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Stable
  4. Final

1. Introduction

The more a communication system grows and increases its diversity, the more likely it is that conflicts arise over which content is acceptable and which is not. In addition, some content may be psychologically triggering or harmful to different people or age groups, while the same content may be desirable to share and talk about in other groups.

This specification intends to provide a machine-readable and extensible way of conveying the kinds and classes of content which are acceptable, and hence to be expected, on a service. Such a service can be an instant messaging account server, a Multi-User Chat (XEP-0045) [1] service or room, a Mediated Information eXchange (MIX) (XEP-0369) [2] service or channel or any other entity which is able to publish extensions as per Service Discovery Extensions (XEP-0128) [3].

The content ratings are provided as a set of free-form strings, scoped by a type URI.

1.1 Prior Art

This idea is not new. The W3C for instance has had two initiatives revolving around labelling content for the web. The Platform for Internet Content Selection (PICS) has been superseded by the Protocol for Web Description Resources (POWDER).

While the PICS approach is roughly similar to what this document intends to achieve, the POWDER standard goes way beyond that and provides much more extension points, at the cost of higher complexity.

Security Labels in XMPP (XEP-0258) [4] provides a way to embed security labels in contexts where clearance to view specific content is required. While the rating of content is roughly similar, the XEP-0258 standard goes beyond that by placing restrictions on entities which carry such labels in a way which is not desirable for this standard.

Specifically, the document states that supporting implementations MUST NOT allow the <securitylabel/> element outside of contexts of specifications known to them, which could pose interoperability issues if that element was reused for this specification.

2. Requirements

3. Glossary

Content Label: A free-form string qualified by a type URI.

Content Rating: A set of Content Labels which describe the describes the classes of content which may be encountered at the entity to which the rating applies.

4. Data Format

The Content Rating is conveyed using a set of free-form strings qualified by a type attribute, the Content Labels.

A Content Label is represented by a single XML <simple-label/> element qualified by the urn:xmpp:crl:0 namespace:

Example 1.
<simple-label xmlns="urn:xmpp:crl:0" type="http://example.com/content-ratings">type-defined string format</simple-label>

The type attribute MUST be a URI. It defines the format of the CDATA contained in the <simple-label/> element. The character data of the <simple-label/> element MUST NOT contain control codes (including newline and horizontal tab).

The type URI must be URL-encoded, escaping all whitespace.

A Content Rating is represented by a <content-rating/> XML element qualified by the urn:xmpp:crl:0 namespace. It carries zero or more <simple-label/> child elements as described above.

Future extensions MAY specify other child elements for <content-rating/> in separate namespaces. See the business rules for an approach for handling those unexpected elements.

4.1 Plain-text compatibility

If the format needs to be conveyed in plain text form, for example to carry the list of labels in Service Discovery Extensions (XEP-0128) [3] or a Data Forms (XEP-0004) [5] configuration form, the following algorithm is to be applied:

5. Use Cases

5.1 Publishing a Content Self-Rating in Service Discovery information

An entity may publish a content self-rating using Service Discovery Extensions (XEP-0128) [3]. For this, a Data Forms (XEP-0004) [5] form with the urn:xmpp:crl:0 FORM_TYPE is defined. All labels are mapped to a single text-multi.

Example 2.
<x type='result' xmlns='jabber:x:data'>
    <field var='FORM_TYPE'>
    <field var='urn:xmpp:crl:0#simple-labels' type='text-multi'>
        <value>http://example.com/content-ratings type-defined string format</value>

Each line in the text-multi field is prefixed with the key of the corresponding <simple-label/> element. The key is followed by a single space character (U+0020), followed by the character data of the <simple-label/> element.

5.2 Offering configuration of the Self-Rating of a XEP-0045 Multi-User-Chat

Entities with sufficient permissions to modify Multi-User Chat (XEP-0045) [1] room configuration SHOULD be offered a text-multi form field of the format described above. If offered this field MUST be mapped to the format described above in the Service Discovery (XEP-0030) [6] response of the room.

6. Business Rules

7. Internationalization Considerations

Implementations which convert the labels to human-readable strings need to translate those strings. For now, no provision is made to provide pre-translated texts.

8. Security Considerations


9. IANA Considerations


10. XMPP Registrar Considerations


11. XML Schema

REQUIRED for protocol specifications.


Appendix A: Document Information

XMPP Standards Foundation
Standards Track
Last Updated
Approving Body
XMPP Council
Superseded By
Short Name

This document in other formats: XML  PDF

Appendix B: Author Information

Jonas Schäfer


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).

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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-0045: Multi-User Chat <https://xmpp.org/extensions/xep-0045.html>.

2. XEP-0369: Mediated Information eXchange (MIX) <https://xmpp.org/extensions/xep-0369.html>.

3. XEP-0128: Service Discovery Extensions <https://xmpp.org/extensions/xep-0128.html>.

4. XEP-0258: Security Labels in XMPP <https://xmpp.org/extensions/xep-0258.html>.

5. XEP-0004: Data Forms <https://xmpp.org/extensions/xep-0004.html>.

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

Appendix H: Revision History

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

  1. Version 0.0.1 (2021-03-03)

    First draft.


Appendix I: Bib(La)TeX Entry

  title = {Content Rating Labels},
  author = {Schäfer, Jonas},
  type = {XEP},
  number = {xxxx},
  version = {0.0.1},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-xxxx.html},
  date = {2021-03-03/2021-03-03},