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  1. 12 IANA considerations
    1. 12.1 text/html
    2. 12.2 text/html-sandboxed
    3. 12.3 application/xhtml+xml
    4. 12.4 text/cache-manifest

11 IANA considerations

11.1 text/html

This registration is for community review and will be submitted to the IESG for review, approval, and registration 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 the name of the character encoding used to serialize the file, must be a valid character encoding name, and must be an ASCII case-insensitive match for the preferred MIME name for that encoding. [IANACHARSET]

Encoding considerations:
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 this specification.
Published specification:
This document is the relevant specification. Labeling a resource with the text/html type asserts that the resource is an HTML document using the HTML syntax.
Applications that use this media type:
Web browsers, tools for processing Web content, HTML authoring tools, search engines, validators.
Additional information:
Magic number(s):
No sequence of bytes can uniquely identify an HTML document. More information on detecting HTML documents is available in the Media Type Sniffing specification. [MIMESNIFF]
File extension(s):
"html" and "htm" are commonly, but certainly not exclusively, used as the extension for HTML documents.
Macintosh file type code(s):
TEXT
Person & email address to contact for further information:
Ian Hickson <ian@hixie.ch>
Intended usage:
Common
Restrictions on usage:
No restrictions apply.
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

Fragment identifiers used with text/html resources refer to the indicated part of the document.

11.2 text/html-sandboxed

This registration is for community review and will be submitted to the IESG for review, approval, and registration with IANA.

Type name:
text
Subtype name:
html-sandboxed
Required parameters:
No required parameters
Optional parameters:
Same as for text/html
Encoding considerations:
Same as for text/html
Security considerations:

The purpose of the text/html-sandboxed MIME type is to provide a way for content providers to indicate that they want the file to be interpreted in a manner that does not give the file's contents access to the rest of the site. This is achieved by assigning the Document objects generated from resources labeled as text/html-sandboxed unique origins.

To avoid having legacy user agents treating resources labeled as text/html-sandboxed as regular text/html files, authors should avoid using the .html or .htm extensions for resources labeled as text/html-sandboxed.

Furthermore, since the text/html-sandboxed MIME type impacts the origin security model, authors should be careful to prevent tampering with the MIME type labeling mechanism itself when documents are labeled as text/html-sandboxed. If an attacker can cause a file to be served as text/html instead of text/html-sandboxed, then the sandboxing will not take effect and a cross-site scripting attack will become possible.

Beyond this, the type is identical to text/html, and the same considerations apply.

Interoperability considerations:
Same as for text/html
Published specification:
This document is the relevant specification. Labeling a resource with the text/html-sandboxed type asserts that the resource is an HTML document using the HTML syntax.
Applications that use this media type:
Same as for text/html
Additional information:
Magic number(s):
Documents labeled as text/html-sandboxed are heuristically indistinguishable from those labeled as text/html.
File extension(s):
"sandboxed"
Macintosh file type code(s):
TEXT
Person & email address to contact for further information:
Ian Hickson <ian@hixie.ch>
Intended usage:
Common
Restrictions on usage:
No restrictions apply.
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

Fragment identifiers used with text/html-sandboxed resources refer to the indicated part of the document.

11.3 application/xhtml+xml

This registration is for community review and will be submitted to the IESG for review, approval, and registration with IANA.

Type name:
application
Subtype name:
xhtml+xml
Required parameters:
Same as for application/xml [RFC3023]
Optional parameters:
Same as for application/xml [RFC3023]
Encoding considerations:
Same as for application/xml [RFC3023]
Security considerations:
Same as for application/xml [RFC3023]
Interoperability considerations:
Same as for application/xml [RFC3023]
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. As such, the relevant specifications are the XML specification, the Namespaces in XML specification, and this specification. [XML] [XMLNS]
Applications that use this media type:
Same as for application/xml [RFC3023]
Additional information:
Magic number(s):
Same as for application/xml [RFC3023]
File extension(s):
"xhtml" and "xht" are sometimes used as extensions for XML resources that have a root element from the HTML namespace.
Macintosh file type code(s):
TEXT
Person & email address to contact for further information:
Ian Hickson <ian@hixie.ch>
Intended usage:
Common
Restrictions on usage:
No restrictions apply.
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

Fragment identifiers used with application/xhtml+xml resources have the same semantics as with any XML MIME type. [RFC3023]

11.4 text/cache-manifest

This registration is for community review and will be submitted to the IESG for review, approval, and registration with IANA.

Type name:
text
Subtype name:
cache-manifest
Required parameters:
No parameters
Optional parameters:
No parameters
Encoding considerations:
Always UTF-8.
Security considerations:

Cache manifests themselves 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 honored. Failure to correctly implement these rules can result in information leakage, cross-site scripting attacks, and the like.

Interoperability considerations:
Rules for processing both conforming and non-conforming content are defined in this specification.
Published specification:
This document is the relevant specification.
Applications that use this media type:
Web browsers.
Additional information:
Magic number(s):
Cache manifests begin with the string "CACHE MANIFEST", followed by either a U+0020 SPACE character, a U+0009 CHARACTER TABULATION (tab) character, a U+000A LINE FEED (LF) character, or a U+000D CARRIAGE RETURN (CR) character.
File extension(s):
"appcache"
Macintosh file type code(s):
No specific Macintosh file type codes are recommended for this type.
Person & email address to contact for further information:
Ian Hickson <ian@hixie.ch>
Intended usage:
Common
Restrictions on usage:
No restrictions apply.
Author:
Ian Hickson <ian@hixie.ch>
Change controller:
W3C

Fragment identifiers have no meaning with text/cache-manifest resources.