12 IANA considerations

12.1 text/html

This registration has been filed successfully with IANA.

Type name:
text
Subtype name:
html
Required parameters:
No required parameters
Optional parameters:
charset

The charset parameter may be provided to definitively specify the document's character encoding, overriding any character encoding declarations in the document. The parameter's value must be one of the labels of the character encoding used to serialize the file. [ENCODING]

Encoding considerations:
8bit (see the section on character encoding declarations)
Security considerations:

Entire novels have been written about the security considerations that apply to HTML documents. Many are listed in this document, to which the reader is referred for more details. Some general concerns bear mentioning here, however:

HTML is scripted language, and has a large number of APIs (some of which are described in this document). Script can expose the user to potential risks of information leakage, credential leakage, cross-site scripting attacks, cross-site request forgeries, and a host of other problems. While the designs in this specification are intended to be safe if implemented correctly, a full implementation is a massive undertaking and, as with any software, user agents are likely to have security bugs.

Even without scripting, there are specific features in HTML which, for historical reasons, are required for broad compatibility with legacy content but that expose the user to unfortunate security problems. In particular, the img element can be used in conjunction with some other features as a way to effect a port scan from the user's location on the Internet. This can expose local network topologies that the attacker would otherwise not be able to determine.

HTML relies on a compartmentalization scheme sometimes known as the same-origin policy. An origin in most cases consists of all the pages served from the same host, on the same port, using the same protocol.

It is critical, therefore, to ensure that any untrusted content that forms part of a site be hosted on a different origin than any sensitive content on that site. Untrusted content can easily spoof any other page on the same origin, read data from that origin, cause scripts in that origin to execute, submit forms to and from that origin even if they are protected from cross-site request forgery attacks by unique tokens, and make use of any third-party resources exposed to or rights granted to that origin.

Interoperability considerations:
Rules for processing both conforming and non-conforming content are defined in the published specification.
Published specification:
http://www.w3.org/TR/html
Applications that use this media type:
Web browsers, tools for processing Web content, HTML authoring tools, search engines, validators.
Fragment identifier considerations:
Fragment identifiers used with text/html resources either refer to the indicated part of the document or provide state information for in-page scripts. Detailed processing for fragment identifiers is defined in the "Navigating to a fragment identifier" section (http://www.w3.org/TR/html/browsers.html#scroll-to-fragid).
Restrictions on usage:
No restrictions apply.
Provisional registration? (standards tree only):
No.
Additional information:
  1. Deprecated alias names for this type: N/A
  2. Magic number(s): No sequence of bytes can uniquely identify an HTML document. More information on detecting HTML documents is available in the MIME Sniffing specification. [MIMESNIFF]
  3. File extension(s): "html" and "htm" are commonly used.
  4. Macintosh file type code: TEXT
  5. Object Identifiers: N/A
Person & email address to contact for further information:
Robin Berjon <robin@berjon.com>
Intended usage:
Common
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

12.2 multipart/x-mixed-replace

This registration has been filed successfully with IANA.

Type name:
multipart
Subtype name:
x-mixed-replace
Required parameters:
Optional parameters:
No optional parameters.
Encoding considerations:
binary
Security considerations:
Subresources of a multipart/x-mixed-replace resource can be of any type, including types with non-trivial security implications such as text/html.
Interoperability considerations:
None.
Published specification:
Rules for processing this type in Web browsers are described in http://www.w3.org/TR/html/browsers.html#read-multipart-x-mixed-replace.
Applications that use this media type:
This type is intended to be used in resources generated by Web servers, for consumption by Web browsers.
Fragment identifier considerations:
Fragment identifiers used with multipart/x-mixed-replace resources apply to each body part as defined by the type used by that body part.
Restrictions on usage:
No restrictions apply.
Provisional registration? (standards tree only):
No.
Additional information:
  1. Deprecated alias names for this type: N/A
  2. Magic number(s): No sequence of bytes can uniquely identify it.
  3. File extension(s): No specific file extensions are recommended for this type.
  4. Macintosh file type code: No specific Macintosh file type codes.
  5. Object Identifiers: N/A
Person & email address to contact for further information:
Robin Berjon <robin@berjon.com>
Intended usage:
Common
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

12.3 application/xhtml+xml

Type name:
application
Subtype name:
xhtml+xml
Required parameters:
None.
Optional parameters:
charset
Same as for application/xml. [RFC7303]
profile
Deprecated as the notion of XHTML profiles has been obsoleted in HTML5. See section 8 of RFC 3236 for additional information about how this parameter was defined.
Encoding considerations:
8bit
Security considerations:
The considerations for "text/html" as specified in http://www.w3.org/TR/html and for 'application/xml' as specified in RFC 7303, also hold for 'application/xhtml+xml'. [RFC7303]
Interoperability considerations:
Rules for processing both conforming and non-conforming content are defined in http://www.w3.org/TR/html.
Published specification:
Labeling a resource with the application/xhtml+xml type asserts that the resource is an XML document that likely has a root element from the HTML namespace. Thus, the relevant specifications are the XML specification, the Namespaces in XML specification, and http://www.w3.org/TR/html. [XML] [XMLNS]
Applications that use this media type:
Web browsers, tools for processing Web content, HTML authoring tools, search engines, validators.
Fragment identifier considerations:
Same as for application/xml. [RFC7303]
Restrictions on usage:
No restrictions apply.
Provisional registration? (standards tree only):
No.
Additional information:
  1. Deprecated alias names for this type: N/A
  2. Magic number(s): No sequence of bytes can uniquely identify an XHTML document. More information on detecting XHTML documents is available in the MIME Sniffing specification. [MIMESNIFF]
  3. File extension(s): "xhtml" and "xht" are sometimes used as extensions for XML resources that have a root element from the HTML namespace.
  4. Macintosh file type code: TEXT.
  5. Object Identifiers: N/A
Person & email address to contact for further information:
Robin Berjon <robin@berjon.com>
Intended usage:
Common
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

12.4 application/x-www-form-urlencoded

This registration has been filed successfully with IANA.

Type name:
application
Subtype name:
x-www-form-urlencoded
Required parameters:
No parameters
Optional parameters:
No parameters
Encoding considerations:
7bit
Security considerations:

In isolation, an application/x-www-form-urlencoded payload poses no security risks. However, as this type is usually used as part of a form submission, all the risks that apply to HTML forms need to be considered in the context of this type.

These risks fall into multiple categories that pertain to the same-origin policy and cross-origin reach of HTML forms (http://www.w3.org/TR/cors/#security), general HTML application threats (http://www.w3.org/TR/html/single-page.html#writing-secure-applications-with-html), and not relying on client-side validation for anything other than user feedback (http://www.w3.org/TR/html/single-page.html#security-forms).

Interoperability considerations:
Rules for generating and processing application/x-www-form-urlencoded payloads are defined in this specification.
Published specification:
http://www.w3.org/TR/html is the relevant specification. Algorithms for encoding and decoding are defined.
Applications that use this media type:
Web browsers and servers.
Fragment identifier considerations:
Fragment identifiers have no meaning with the application/x-www-form-urlencoded type.
Restrictions on usage:
This type is only intended to be used to describe HTML form submission payloads.
Provisional registration? (standards tree only):
No.
Additional information:
  1. Deprecated alias names for this type: N/A
  2. Magic number(s): There is no reliable mechanism for recognising such payloads.
  3. File extension(s): N/A
  4. Macintosh file type code: N/A.
  5. Object Identifiers: N/A
Person & email address to contact for further information:
Robin Berjon <robin@berjon.com>
Intended usage:
Common
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

12.5 text/cache-manifest

This registration has been filed successfully with IANA.

Type name:
text
Subtype name:
cache-manifest
Required parameters:
No parameters
Optional parameters:
charset

The charset parameter may be provided. The parameter's value must be "utf-8". This parameter serves no purpose; it is only allowed for compatibility with legacy servers.

Encoding considerations:
8bit
Security considerations:

Cache manifests themselves contain no executable content and pose no immediate risk unless sensitive information is included within the manifest.

Implementations however, are required to follow specific rules when populating a cache based on a cache manifest, to ensure that certain origin-based restrictions are honoured. Failure to correctly implement these rules can result in information leakage, cross-site scripting attacks, and the like.

Caching mechanisms are typically subjects of poisoning attacks and the one that this file type supports is no exception. The published specification includes steps intended to mitigate such issues (notably non-malicious cache poisoning from captive portals) but implementers are advised to exercise caution in caching.

Additionally, the permanence of this caching mechanism requires care to be taken with respect to users' privacy (http://www.w3.org/TR/html/single-page.html#expiring-application-caches) and storage resources (http://www.w3.org/TR/html/single-page.html#disk-space).

Interoperability considerations:
Rules for processing both conforming and non-conforming content are defined in the HTML specification.
Published specification:
http://www.w3.org/TR/html/ is the relevant specification.
Applications that use this media type:
Web browsers.
Fragment identifier considerations:
Fragment identifiers have no meaning with the text/cache-manifest type.
Restrictions on usage:
No restrictions apply.
Provisional registration? (standards tree only):
No.
Additional information:
  1. Deprecated alias names for this type: N/A
  2. Magic number(s): "CACHE MANIFEST" followed by [ \t\r\n]
  3. File extension(s): "appcache", "manifest"
  4. Macintosh file type code: No specific Macintosh file type codes are recommended.
  5. Object Identifiers: N/A
Person & email address to contact for further information:
Robin Berjon <robin@berjon.com>
Intended usage:
Common
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

12.6 web+ scheme prefix

This section describes a convention for use with the IANA URI scheme registry. It does not itself register a specific scheme. [RFC4395]

URI scheme name:
Schemes starting with the four characters "web+" followed by one or more letters in the range a-z.
Status:
permanent
URI scheme syntax:
Scheme-specific.
URI scheme semantics:
Scheme-specific.
Encoding considerations:
All "web+" schemes should use UTF-8 encodings where relevant.
Applications/protocols that use this URI scheme name:
Scheme-specific.
Interoperability considerations:
The scheme is expected to be used in the context of Web applications.
Security considerations:
Any Web page is able to register a handler for all "web+" schemes. As such, these schemes must not be used for features intended to be core platform features (e.g. network transfer protocols like HTTP or FTP). Similarly, such schemes must not store confidential information in their URLs, such as usernames, passwords, personal information, or confidential project names.
Contact:
Ian Hickson <ian@hixie.ch>
Author/Change controller:
Ian Hickson <ian@hixie.ch>
References:
Custom scheme and content handlers, HTML Living Standard: http://www.whatwg.org/specs/web-apps/current-work/#custom-handlers