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Internet-Draft This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. About This Document Status information for this document may be found at . information can be found at . Source for this draft and an issue tracker can be found at .

Introduction Internet application protocols are capable of carrying arbitrary labeled content, including but not limited to HTTP and MIME . Such labels are known as media types. A media type consists of a top-level type and a subtype, which is further structured into trees. Optionally, a media type can be defined to allow companion data, known as parameters. This document defines the criteria and procedures to be used to register media types () as well as media type structured suffixes () in the Internet Assigned Numbers Authority (IANA) registry. The location of the media type registry managed by these procedures is:

• http://www.iana.org/assignments/media-types/

Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in when they appear in ALL CAPS. They may also appear in lower or mixed case as plain English words, without any normative meaning. This specification makes use of the Augmented Backus-Naur Form (ABNF) notation, including the core rules defined in Appendix B of that document.

Media Type Registration Requirements Media type registrations are expected to conform to various requirements laid out in the following sections. Note that specific requirements can vary depending on the registration tree. Additional requirements specific to the registration of XML media types are specified in .

Functionality Media types MUST function as actual media formats. Registration of things that are better thought of as a transfer encoding, as a charset, or as a collection of separate entities of another type, is not allowed. For example, although applications exist to decode the base64 transfer encoding , base64 cannot be registered as a media type. This requirement applies regardless of the registration tree involved.

Publication Media types registered in the standards tree by the IETF MUST be published as RFCs. RFC publication of vendor and personal media type registrations is allowed but not required. In all cases, the IANA will retain copies of all media type registrations and publish them as part of the media types registration tree itself. Standards-tree registrations for media types defined in documents produced by other standards-related organizations MUST be described by a formal standards specification produced by that organization. Additionally, any copyright on the registration template MUST allow the IANA to copy it into the IANA registry. The standards tree exists for those media types that require a substantive review and approval process in a recognized standards-related organization. The vendor and personal trees exist for those media types that do not require such a process. It is expected that applicability statements for particular applications will be published from time to time in the IETF, recommending implementation of, and support for, media types that have proven particularly useful in those contexts. Other than IETF registrations in the standards tree, the registration of a media type does not imply endorsement, approval, or recommendation by the IANA or the IETF or even certification that the specification is adequate. Registration of a top-level type requires Standards Action in the IETF and, hence, the publication of a RFC on the Standards Track.

Availability A permanent and readily available public specification of the format for the media type MUST exist for all types registered in the standards tree. This specification MUST provide sufficient detail so that interoperability between independent implementations using the media type is possible. If not part of the media type registration proposal, this specification MUST be referenced by it. The specifications of format and processing particulars need not be publicly available for media types registered in the vendor and personal trees. Such registrations are explicitly permitted to limit the information in the registration to which software and version produce or process such media types. As such, references to or inclusion of format specifications in registrations is encouraged but not required. Note, however, that the public availability of a meaningful specification will often make the difference between simply having a name reserved so that there are no conflicts with other uses and having the potential for other implementations of the media type and useful interoperation with them.

Intellectual Property The registration of media types involving patented technology is permitted. However, the restrictions set forth in BCP 79 and BCP 78 on the use of patented technology in IETF Standards Track protocols must be respected when the specification of a media type is part of a Standards Track protocol. In addition, other standards-related organizations making use of the standards tree may have their own rules regarding intellectual property that must be observed in their registrations. Intellectual Property Rights (IPR) disclosures for registrations in the vendor and personal trees are encouraged but not required.

Canonicalization and Interoperability All registered media types MUST employ a single, canonical data format, regardless of registration tree. Ideally, media types will be defined so they interoperate across as many systems and applications as possible. However, some media types will inevitably have problems interoperating across different platforms. For example, problems with different versions, byte ordering, and specifics of gateway handling can arise. Universal interoperability of media types is not required, but known interoperability issues SHOULD be identified whenever possible. Publication of a media type does not require an exhaustive review of interoperability, and the interoperability considerations section is subject to continuing evaluation. The recommendations in this subsection apply regardless of the registration tree involved.

Naming All registered media types MUST be assigned top-level type and subtype names. The combination of these names serves to uniquely identify the media type, and the subtype name facet (or the absence of one) identifies the registration tree. Both top-level type and subtype names are case-insensitive. Type and subtype names MUST conform to the following ABNF: Note that this syntax is somewhat more restrictive than what is allowed by or . Also note that while this syntax allows names of up to 127 characters, implementation limits may make such long names problematic. For this reason, 'type-name' and 'subtype-name' SHOULD be limited to 64 characters. Although this syntax treats "." as equivalent to any other character, characters before any initial "." always specify the registration facet. Note that this means that facet-less standards tree registrations cannot use periods in the subtype name. Similarly, the final "+" in a subtype name introduces a structured syntax specifier suffix. Structured syntax suffix requirements are specified in . While it is possible for a given media type to be assigned more than one name, the use of different names to identify the same media type is discouraged. These requirements apply regardless of the registration tree involved.

Aliases In some cases, a single media type may have been widely deployed prior to registration under multiple names. In such cases, a preferred name MUST be chosen for the media type, and applications MUST use this to be compliant with the type's registration. However, a list of deprecated aliases by which the type is known MAY be supplied as additional information in order to assist applications in processing the media type properly.

Parameters Media types MAY be defined to allow or require use of media type parameters. Additionally, some parameters may be automatically made available to the media type by virtue of being a subtype of a content type that defines a set of parameters applicable to any of its subtypes. In either case, the names, values, and meanings of any parameters MUST be fully specified when a media type is registered in the standards tree, and SHOULD be specified as completely as possible when media types are registered in the vendor or personal trees. Parameter names have the same syntax as media type names and values: Note that this syntax is somewhat more restrictive than what is allowed by the ABNF in and amended by . Parameter names are case-insensitive and no meaning is attached to the order in which they appear. It is an error for a specific parameter to be specified more than once. There is no defined syntax for parameter values; therefore, it MUST be specified upon registration. Additionally, some transports impose restrictions on parameter value syntax, so care needs be taken to limit the use of potentially problematic syntaxes; for example, binary valued parameters, while permitted in some protocols, are best avoided. Note that a protocol can impose further restrictions on parameter value syntax, depending on how it chooses to represent parameters. Both MIME and HTTP allow binary parameters as well as parameter values expressed in a specific charset, but other protocols may be less flexible. Types already registered in the standards tree SHOULD NOT have new functionality added through the definition of new parameters subsequent to the original registration. New parameters MAY be used to convey additional information that does not otherwise change existing functionality. An example of this would be a "revision" parameter to indicate a revision level of an external specification such as JPEG. Similar behavior is encouraged for media types registered in the vendor or personal trees, but is not required. Changes to parameters (including the introduction of new ones) is managed in the same manner as other changes to the media type; see .

Encoding Some transports impose restrictions on the type of data they can carry. For example, Internet mail traditionally was limited to 7bit US-ASCII text. Encoding schemes are often used to work around such transport limitations. It is therefore useful to note what sort of data a media type can consist of as part of its registration. An "encoding considerations" field is provided for this purpose. Possible values of this field are:

7bit:

The content of the media type consists solely of CRLF- delimited 7bit US-ASCII text.

8bit:

The content of the media type consists solely of CRLF- delimited 8bit text.

binary:

The content consists of an unrestricted sequence of octets.

framed:

The content consists of a series of frames or packets without internal framing or alignment indicators. Additional out- of-band information is needed to interpret the data properly, including but not necessarily limited to knowledge of the boundaries between successive frames and knowledge of the transport mechanism. Note that media types of this sort cannot simply be stored in a file or transported as a simple stream of octets; therefore, such media types are unsuitable for use in many traditional protocols. A commonly used transport with framed encoding is the Real-time Transport Protocol, RTP. Additional rules for framed encodings defined for transport using RTP are given in .

Additional restrictions on 7bit and 8bit text are given in .

Fragment Identifiers Media type registrations can specify how applications should interpret fragment identifiers (specified in ) associated with the media type. Media types are encouraged to adopt fragment identifier schemes that are used with semantically similar media types. In particular, media types that use a named structured syntax with a registered "+suffix" MUST follow whatever fragment identifier rules are given in the structured syntax suffix registration.

Security All registrations of types in the standards tree MUST include an analysis of security issues. A similar analysis for media types registered in the vendor or personal trees is encouraged but not required. All descriptions of security issues MUST be as accurate as possible regardless of registration tree. In particular, the security considerations MUST NOT state that there are "no security issues associated with this type". Security considerations for types in the vendor or personal tree MAY say that "the security issues associated with this type have not been assessed". There is no requirement that media types registered in any tree be secure or completely free from risks. Nevertheless, all known security risks MUST be identified in the registration of a media type, again regardless of registration tree. The security considerations section of all registrations is subject to continuing evaluation and modification, and in particular MAY be extended by use of the "comments on media types" mechanism described in below. Some of the issues that need to be examined and described in a security analysis of a media type are:

• Processing of complex media types might institute actions on a recipient's files or other resources. If it is possible to specify arbitrary actions in an unrestricted fashion, it could have devastating effects. See the registration of the application/postscript media type in for an example of description and handling of these issues.
• Any security analysis MUST state whether or not the format employs such "active content"; if it does, it MUST state what steps have been taken (or are required be taken by applications) of the media type to protect users of the media type.
• Processing of complex media types might institute actions that, while not directly harmful to the recipient, may result in disclosure of information that either facilitates a subsequent attack or else violates a recipient's privacy in some way. Again, the registration of the application/ postscript media type illustrates how such directives can be handled.
• A media type that employs compression may provide an opportunity for sending a small amount of data that, when received and evaluated, expands enormously to consume all of the recipient's resources. All media types SHOULD state whether or not they employ compression; if they do, they SHOULD discuss what steps need to be taken to avoid such attacks.
• A media type might be targeted for applications that require some sort of security assurance but don't provide the necessary security mechanisms themselves. For example, a media type could be defined for storage of sensitive medical information that in turn requires external confidentiality and integrity protection services, or which is designed for use only within a secure environment. Types SHOULD always document whether or not they need such services in their security considerations.

Structured Suffixes

Document Validity If a toolchain chooses to process a provided media type by using the selected structured suffix processing rules, it cannot presume that a document that is valid per the decoding rules associated with the structured suffix will be valid for a recognized subset of the structured suffix. For example, presuming a media type of "application/foo+bar", a toolchain cannot presume that a valid "+bar" document will also be a valid "application/foo" document. On the other hand, presuming a media type of "application/foo+bar", a toolchain can presume that a valid "application/foo+bar" document will also be a valid "+bar" document.

Fragment Semantics If a toolchain chooses to process a provided media type by using the selected structured suffix processing rules, it cannot presume that fragment identifier semantics will be the same across a recognized subset of the structured suffix. For example, presuming a media type of "application/foo+bar", a toolchain cannot presume that the fragment semantics for a "+bar" document will be the same as for an "application/foo+bar" document.

Security Characteristics Toolchains cannot assume that the security characteristics of processing based on structured suffixes will be the same for the entire media type. For example, presuming a media type of "application/foo+bar", a toolchain cannot presume that the security characteristics for a "+bar" document will be the same as for a "application/foo+bar" document.

Partial Processing It is conceivable that an attacker could utilize structured suffixes in a way that tricks unsuspecting toolchains into skipping important security checks and allowing viruses to propagate. For example, an attacker might utilize an "application/vnd.ms-excel.addin.macroEnabled.12+zip" structured suffix to trigger an unzip process that might then directly invoke Microsoft Excel, bypassing anti-virus tooling that would otherwise block a macro-enabled MS Excel file containing a virus of some kind from being scanned or opened. Enterprising attackers might take advantage of toolchains that partially process media types in this manner. Toolchains that process media types based purely on a structured suffix need to ensure that further processing does not blindly trust the decoded data, and that proper magic header or file structure checking is performed, before allowing the decoded data to drive operations that might negatively impact the application environment or operating system.

Non-Requirements In the asynchronous mail environment, where information on the capabilities of the remote mail agent is frequently not available to the sender, maximum interoperability is attained by restricting the media types used to those "common" formats expected to be widely implemented. This was asserted in the past as a reason to limit the number of possible media types, and resulted in a registration process with a significant hurdle and delay for those registering media types. However, the need for "common" media types does not require limiting the registration of new media types. If a limited set of media types is recommended for a particular application, that should be asserted by a separate applicability statement specific for the application and/or environment. Therefore, universal support and implementation of a media type are NOT a requirement for registration. However, if a media type is explicitly intended for limited use, this MUST be noted in its registration. The "Restrictions on Usage" field is provided for this purpose.

Additional Information The following optional information SHOULD be included in the specification of a media type if it is available:

• Magic number(s) (length, octet values). Magic numbers are byte sequences that are always present at a given place in the file and thus can be used to identify entities as being of a given media type.
• File name extension(s) commonly used on one or more platforms to indicate that some file contains a given media type.
• macOS Uniform Type Identifier (a string), if it makes sense to exchange media of this type through user-triggered exchange mechanisms such as copy-and-paste or drag-and-drop on macOS and related platforms (see for definitions and syntax).
• Windows clipboard name (a string), if it makes sense to exchange media of this type through user-triggered exchange mechanisms such as copy-and-paste or drag-and-drop on Microsoft Windows and related platforms (see for definitions and syntax).

In the case of a registration in the standards tree, this additional information MAY be provided in the formal specification of the media type format. It is suggested that this be done by incorporating the IANA media type registration form into the format specification itself.

Top-Level Media Types The choice of top-level type MUST take into account the nature of media type involved. New subtypes of top-level types MUST conform to the restrictions of the top-level type, if any. The following sections describe each of the initial set of top-level types and their associated restrictions. Additionally, various protocols, including but not limited to HTTP and MIME, MAY impose additional restrictions on the media types they can transport. (See for additional information on the restrictions MIME imposes.)

Text Media Types A top-level type of "text" indicates that the content is principally textual in form. Text that does not provide for or allow formatting commands, font attribute specifications, processing instructions, interpretation directives, or content markup is known as "plain text". Plain text is seen simply as a linear sequence of characters, possibly interrupted by line breaks or page breaks. Plain text MAY allow the stacking of several characters in the same position in the text. Plain text in scripts like Arabic and Hebrew may also include facilities that allow the arbitrary mixing of text segments with different writing directions. Beyond plain text, there are many formats for representing what might be known as "rich text". An interesting characteristic of many such representations is that they are to some extent readable even without the software that interprets them. It is useful to distinguish them, at the highest level, from such unreadable data as images, audio, or text represented in an unreadable form. In the absence of appropriate interpretation software, it is reasonable to present subtypes of "text" to the user, while it is not reasonable to do so with most non-textual data. Such formatted textual data can be represented using subtypes of "text".

The Charset Parameter Many subtypes of text, notably including the subtype "text/plain", which is a generic subtype for plain text defined in , define a "charset" parameter. If a "charset" parameter is defined for a particular subtype of text, it MUST be used to specify a charset name defined in accordance to the procedures laid out in . As specified in , a "charset" parameter SHOULD NOT be specified when charset information is transported inside the payload (e.g., as in "text/xml"). If a "charset" parameter is specified, it SHOULD be a required parameter, eliminating the options of specifying a default value. If there is a strong reason for the parameter to be optional despite this advice, each subtype MAY specify its own default value, or alternatively, it MAY specify that there is no default value. Finally, the "UTF-8" charset SHOULD be selected as the default. See for additional information on the use of "charset" parameters in conjunction with subtypes of text. Regardless of what approach is chosen, all new text/* registrations MUST clearly specify how the charset is determined; relying on the US-ASCII default defined in is no longer permitted. If explanatory text is needed, this SHOULD be placed in the additional information section of the registration.

Image Media Types A top-level type of "image" indicates that the content is one or more individual images. The subtype names the specific image format.

Audio Media Types A top-level type of "audio" indicates that the content is audio data. The subtype names the specific audio format.

Video Media Types A top-level type of "video" indicates that the content is a time-varying-picture image, possibly with color and coordinated sound. The term 'video' is used in its most generic sense, rather than with reference to any particular technology or format, and is not meant to preclude subtypes such as animated drawings encoded compactly. Note that although in general the mixing of multiple kinds of media in a single body is discouraged , it is recognized that many video formats include a representation for synchronized audio and/or text, and this is explicitly permitted for subtypes of "video".

Application Media Types A top-level type of "application" indicates that the content is discrete data that do not fit under any of the other type names, and particularly for data to be processed by some type of application program. This is information that must be processed by an application before it is viewable or usable by a user. Expected uses for the "application" type name include but are not limited to file transfer, spreadsheets, presentations, scheduling data, and languages for "active" (computational) material. (The last, in particular, can pose security problems that must be understood by implementors. The "application/postscript" media type registration in provides a good example of how to handle these issues.) For example, a meeting scheduler might define a standard representation for information about proposed meeting dates. An intelligent user agent would use this information to conduct a dialog with the user, and might then send additional material based on that dialog. More generally, there have been several "active" languages developed in which programs in a suitably specialized language are transported to a remote location and automatically run in the recipient's environment. Such applications may be defined as subtypes of the "application" top-level type. The subtype of "application" will often either be the name or include part of the name of the application for which the data are intended. This does not mean, however, that any application program name may simply be used freely as a subtype of "application"; the subtype needs to be registered.

Multipart and Message Media Types A top-level type of "multipart" or "message" indicates that the content is a composite type; that is, they provide a means of encapsulating zero or more objects, each one a separate media type. All subtypes of multipart and message MUST conform to the syntax rules and other requirements specified in and amended by .

Additional Top-Level Types In some cases, a new media type may not be easily classified under any currently defined top-level type names. Such cases are expected to be quite rare. However, if such a case does arise, a new type name can be defined to accommodate it. Definition of a new top-level type name MUST be done via a Standards Track RFC, taking into account the criteria and guidelines given below; no other mechanism can be used to define additional type names.

Required Criteria Definitions of new top-level types are required to fulfil the following criteria:

• Every new top-level type MUST be defined in a Standards Track RFC (see ). This will make sure there is sufficient community interest, review, and consensus appropriate for a new top-level type.
• The IANA Considerations section of an RFC defining a new top-level type MUST request that IANA add this new top-level type to the registry of top-level types.
• The criteria for what types do and do not fall under the new top-level type MUST be defined clearly. Clear criteria are expected to help expert reviewers to evaluate whether a subtype belongs below the new type or not, and whether the registration template for a subtype contains the appropriate information. If the criteria cannot be defined clearly, this is a strong indication that whatever is being talked about is not suitable as a top-level type.
• Any RFC defining a new top-level type MUST clearly document the security considerations applying to all or a significant subset of subtypes.
• At the minimum, one subtype MUST be described. A top-level type without any subtype serves no purpose. Please note that the 'example' top-level describes a subtype 'example'.

Additional Considerations Additional considerations for the defintion of a new top-level type include:

• Existing wide use of an unregistered top-level type may be an indication of a need, and therefore an argument for formally defining a new top-level type.
• On the other hand, the use of unregistered top-level types is highly discouraged.
• Use of an IETF Working Group to define a new top-level type is not needed, but may be advisable in some cases. There are examples of new top-level type definitions without a Working Group (), with a short, dedicated WG (), and with a Working Group that included other related work ().
• The document defining the new top-level type should include initial registrations of actual subtypes. The exception may be a top-level type similar to 'example'. This will help to show the need for the new top-level type, will allow checking the appropriateness of the definition of the new top-level type, will avoid separate work for registering an initial slate of subtypes, and will provide examples of what is considered a valid subtype for future subtype registrations.
• The registration and actual use of a certain number of subtypes under the new top-level type should be expected. The existence of a single subtype should not be enough; it should be clear that new similar types may appear in the future. Otherwise, the creation of a new top-level type is likely unjustified.
• The proposers of the new top-level type and the wider community should be willing to commit to emitting and consuming the new top-level type in environments that they control.
• The fact that a group of (potential) types have (mostly) common parameters may be an indication that these belong under a common new top-level type.
• Top-level types can help humans with understanding and debugging. Therefore, evaluating how a new top-level type helps humans understand types may be crucial.
• Common restrictions may apply to all subtypes of a top-level type. Examples are the restriction to CRLF line endings for subtypes of type 'text' (at least in the context of electronic mail), or on subtypes of type 'multipart'.
• Top-level types are also used frequently in dispatching code. For example "multipart/*" is frequently handled as multipart/mixed, without understanding of a specific subtype. The top-level types 'image', 'audio', and 'video' are also often handled generically. Documents with these top-level types can be passed to applications handling a wide variety of image, audio, or video formats. HTML generating applications can select different HTML elements (e.g. <img> or <audio>) for including data of different top-level types. Applications can select different icons to represent unknown types in different top-level types.

Negative Criteria Negative indicators for creation of a new top-level type include:

• A top-level type is not a pointer into another registration space that offers duplicate registrations for existing media types. Example: a top-level type of 'oid', leading to types of the form oid/nnnnn, where nnn is an OID (Object Identifier) designating a specific media format,
• A top-level type MUST NOT be defined for the mapping of other protocol elements to media types. For example, while there may be some merit to a mapping from media types to URIs, e.g. in the context of RDF (Resource Description Framework), there is very limited merit in a reverse mapping, and even less merit in creating a top-level type for such a mapping. The same applies to other protocol elements such as file extensions or URI schemes. The recommended solution in case a mapping is needed is to choose a single type/subtype and put the additional information in an appropriately named parameter. As an example, information on a file extension '.dcat' can be encoded as 'application/octet-string; filename=foo.dcat'.
• Media types are not a general type system. A top-level type MUST NOT be defined if its main or only purpose is to map other type systems, e.g. in programming languages or ontologies.
• A new top-level type SHOULD NOT generate aliases for existing widely used types or subtypes.
• Top-level types with an "X-" prefix cannot be registered, and SHOULD NOT be used. See .

Media Subtypes

Registration Trees In order to increase the efficiency and flexibility of the registration process, different structures of subtype names can be registered in distinct "trees," distinguished with faceted names. For example, a subtype that is recommended for wide support and implementation by the Internet community would be registered in the Standards Tree and not have a prefix, while a subtype that is used to move files associated with proprietary software would be registered in the Vendor Tree, and so its name would begin with a "vnd." prefix. Note that some previously defined media types do not conform to the naming conventions described below. See for a discussion of them.

Standards Tree The standards tree is intended for types of general interest to the Internet community. Registrations in the standards tree MUST be either:

1. in the case of registrations associated with IETF specifications, approved directly by the IESG, or
2. registered by a recognized standards-related organization using the "Specification Required" IANA registration policy (which implies Expert Review), or
3. approved by the Designated Expert(s) as identifying a "community format", as described in .

The first procedure is used for registrations from IETF Consensus documents, or in rare cases when registering a grandfathered (see ) and/or otherwise incomplete registration is in the interest of the Internet community. The registration proposal MUST be published as an RFC. When the registration RFC is in the IETF stream, it must have IETF Consensus. Registrations published in non-IETF RFC streams are also allowed, but require IESG approval. A registration can be either in a stand-alone "registration only" RFC or incorporated into a more complete specification. In the second case, the IESG makes a one-time decision on whether the registration submitter represents a recognized standards-related organization; after that, a Media Types Reviewer (Designated Expert or a group of Designated Experts) performs the Expert Review as specified in this document. Subsequent submissions from the same source do not involve the IESG. The format MUST be described by a formal standards specification produced by the submitting standards-related organization. The third case is described in . Media types in the standards tree MUST NOT have faceted names, unless they are grandfathered in using the process described in . The change controller of a media type registered in the standards tree is assumed to be the standards-related organization itself. Modification or alteration of the specification uses the same level of processing (e.g., a registration submitted on Standards Track can be revised in another Standards Track RFC, but cannot be revised in an Informational RFC) required for the initial registration. Standards-tree registrations from recognized standards-related organizations are submitted directly to the IANA, where they will undergo Expert Review prior to approval. In this case, the Expert Reviewer(s) will, among other things, ensure that the required specification provides adequate documentation.

Community Formats in the Standards Tree Some formats are interoperable (i.e., they are supported by more than one implementation), but their specifications are not published by a recognized standards-related organization. To accommodate these cases, the Designated Expert(s) are empowered to approve registrations in the standards tree that meet the following criteria:

• There is a well-defined specification for the format
• That specification is not tied to or heavily associated with one implementation
• The specification is freely available at a stable location
• There are multiple interoperable implementations of the specification, or they are likely to emerge
• The requested name is appropriate to the use case, and not so generic that it may be considered 'squatting'
• There is no conflict with IETF work or work at other recognised SDOs (present or future)
• There is evidence of broad adoption

The Designated Expert(s) have discretion in applying these criteria; in rare cases, they might judge it best to register an entry that fails one or more. Note that such registrations still go through preliminary community review (Section 5.1), and decisions can be appealed (Section 5.3).

Vendor Tree The vendor tree is intended for media types associated with publicly available products. "Vendor" and "producer" are construed very broadly in this context, and are considered equivalent. Note that industry consortia as well as non-commercial entities that do not qualify as recognized standards-related organizations can register media types in the vendor tree. A registration may be placed in the vendor tree by anyone who needs to interchange files associated with some product or set of products. However, the registration properly belongs to the vendor or organization producing the software that employs the type being registered, and that vendor or organization can at any time elect to assume change control of a registration done by a third party in order to correct or update it. See for additional information. When a third party registers a type on behalf of someone else, both entities SHOULD be noted in the Change Controller field in the registration. One possible format for this would be "Foo, on behalf of Bar". Vendor tree registrations are distinguished by the leading facet "vnd.". That may be followed, at the discretion of the registrant, by either a media subtype name from a well-known producer (e.g., "vnd.mudpie") or by an IANA-approved designation of the producer's name that is followed by a media type or product designation (e.g., vnd.bigcompany.funnypictures). While public exposure and review of media types to be registered in the vendor tree are not required, requesting review on the media-types@iana.org mailing list is encouraged, to improve the quality of those specifications. Registrations in the vendor tree may be submitted directly to the IANA, where they will undergo Expert Review prior to approval.

Personal Tree The personal tree is intended for media types created experimentally or as part of products that are not distributed commercially. This tree is sometimes referred to as the "vanity" tree. Personal tree registrations are distinguished by the leading facet "prs.". The change controller of a "personal" registration is the person or entity making the registration, or one to whom responsibility has been transferred as described below. While public exposure and review of media types to be registered in the personal tree are not required, requesting review on the media-types@iana.org mailing list is encouraged, to improve the quality of those specifications. Registrations in the personal tree may be submitted directly to the IANA, where they will undergo Expert Review prior to approval.

Unregistered x. Tree Subtype names with "x." as the first facet are intended exclusively for use in private, local environments. Subtypes using this tree cannot be registered and are intended for use only with the active agreement of the parties exchanging them. The low barrier to registration in the vendor and personal trees means it should rarely, if ever, be necessary to use unregistered types. Therefore, use of types in the "x." tree is strongly discouraged. Note that types with names beginning with "x-" are no longer considered to be members of this tree (see ). Also note that if a generally useful and widely deployed type incorrectly uses an "x-" name prefix, it MAY be registered using its current name in an alternative tree by following the procedure defined in .

Additional Registration Trees From time to time and as required by the community, new top-level registration trees may be created by IETF Standards Action. It is explicitly assumed that these trees may be created for external registration and management by well-known permanent organizations; for example, scientific societies may register media types specific to the sciences they cover. In general, the quality of review of specifications for one of these additional registration trees is expected to be equivalent to registrations in the standards tree by a recognized standards-related organization. When the IETF performs such review, it needs to consider the greater expertise of the requesting organization with respect to the subject media type.

Subtype Suffixs standardized a suffix convention for well-known structured syntaxes. In particular, media types have been registered with suffixes such as "+der", "+fastinfoset", and "+json". A structured suffix is defined as all of the characters to the right of the left-most "+" sign in a media type, including the left-most "+" sign itself. The structured suffix MUST NOT contain more than one "+" sign. As an example, given the "application/foo+bar" media type: "application" is the top-level type, "foo" is the base subtype name, and "+bar" is the structured suffix. A media type such as "application/foo+bar+baz" is not allowed. The primary guideline for whether a structured type name suffix is registrable is that it be described by a readily available description, preferably within a document published by an established standards-related organization, and for which there's a reference that can be used in a Normative References section of an RFC. Media types that make use of a named structured syntax SHOULD use the appropriate registered "+suffix" for that structured syntax when they are registered. By the same token, media types MUST NOT be given names incorporating suffixes for structured syntaxes they do not actually employ. "+suffix" constructs for as-yet unregistered structured syntaxes SHOULD NOT be used, given the possibility of conflicts with future suffix definitions. Media types that make use of a named structured syntax, or similar separator such as a dash "-", MUST ensure that the registration is semantically aligned, from a data model perspective, with existing base subtype names in the media type registry. For example, for the media types "application/foo+bar" and "application/foo+baz", the expectation is that the semantics suggested by the base subtype name "application/foo" are the same between both media types. The Designated Expert MUST reject a registration if they believe the semantics for a media type registration does not align with existing base subtype names in the media type registry. Registrants MUST prove to the Designated Expert, such as through an email to a public mailing list or issue tracker comment, that they have consent from the existing change controller for the associated base subtype name to register the new media type.

Common Suffix Patterns There are a few common patterns that are utilized for media types that use structured suffixes. These patterns include expressing that the data associated with a media type:

• Utilizes a structured data format such as "+xml", "+json", "+yaml", or "+cbor".
• Is compressed using a binary compression format such as "+zip" or "+gzip".
• Is encoded in a digitally signature format such as "+jwt" or "+cose".

While it is conceivable that suffixes such as "+xml+zip" are possible, such usage is NOT RECOMMENDED due to the large number of combinatorial possibilities that could occur and the negative impact that might have on security considerations for toolchains that attempt to safely process all of the possibilities.

Fragment Identifiers and Suffixes The syntax and semantics for fragment identifiers are specified in the "Fragment Identifier Considerations" column in the IANA Structured Syntax Suffixes registry. In general, when processing fragment identifiers associated with a structured syntax suffix, the following rules SHOULD be followed:

1. For cases defined for the structured syntax suffix, where the fragment identifier does resolve per the structured syntax suffix rules, then proceed as specified by the specification associated with the "Fragment Identifier Considerations" column in the IANA Structured Syntax Suffixes registry.
2. For cases defined for the structured syntax suffix, where the fragment identifier does not resolve per the structured syntax suffix rules, then proceed as specified by the specification associated with the full media type.
3. For cases not defined for the structured syntax suffix, then proceed as specified by the specification associated with the full media type.

Media Type Registration Procedures The media type registration procedure is not a formal standards process, but rather an administrative procedure intended to allow community comment and sanity checking without excessive time delay. Normal IETF processes need to be followed for all IETF registrations in the standards tree. The posting of an Internet Draft is a necessary first step, followed by posting to the media-types@iana.org list as discussed below.

Preliminary Community Review Notice of a potential media type registration in the standards tree SHOULD be sent to the media-types@iana.org mailing list for review. Registrations in other trees MAY be sent to the list for review as well; doing so is entirely OPTIONAL, but is strongly encouraged. The purpose of this notification is to solicit comments and feedback on the choice of type/subtype name, the unambiguity of the references with respect to versions and external profiling information, and a review of any interoperability or security considerations. The submitter may submit a revised registration proposal or abandon the registration completely and at any time.

Submit Request to IANA Media types registered in the standards tree by the IETF itself MUST be reviewed and approved by the IESG as part of the normal standards process. Standards-tree registrations by recognized standards-related organizations as well as registrations in the vendor and personal trees are submitted directly to the IANA, unless other arrangements were made as part of a liaison agreement. Registration requests can be sent to iana@iana.org. A web form for registration requests is also available at:

• http://www.iana.org/form/media-types

Provisional Registrations Standardization processes often take considerable time to complete. In order to facilitate prototyping and testing, it is often helpful to assign media types early in the process. This way, identifiers used during standards development can remain unchanged once the process is complete, and implementations and documentation do not have to be updated. Accordingly, provisional registrations of media type names in the standards tree MAY be submitted to IANA. The only required fields in such registrations are the media type name and contact information (including the standards-related organization name). Upon receipt of a provisional registration, IANA will check the name and contact information, then publish the registration in a distinct, publicly-visible provisional registration list. Provisional registrations MAY be updated or abandoned at any time. When the registration is abandoned, the media type is no longer registered in any sense; it can subsequently be registered just like any other unassigned media type name.

Review and Approval With the exception of provisional standards-tree registrations, registrations submitted to the IANA will be first given to the media types reviewer, who is appointed by the IETF Applications Area Director(s). The media types reviewer examines registration requests to make sure they meet the requirements set forth in this document. Decisions made by the media types reviewer may be appealed to the IESG using the procedure specified in . Once a media type registration has passed review, the IANA will register the media type and make the media type registration available to the community. In the case of standards-tree registrations from other standards-related organizations, IANA will also check that the submitter is in fact a recognized standards-related organization. If the submitter is not currently recognized as such, the IESG will be asked to confirm their status. Recognition from the IESG MUST be obtained before a standards-tree registration can proceed.

Comments on Media Type Registrations Comments on registered media types may be submitted by members of the community to the IANA at iana@iana.org. These comments will be reviewed by the media types reviewer and then passed on to the change controller of the media type if possible. Submitters of comments may request that their comment be attached to the media type registration itself; if the IANA, in consultation with the media types reviewer, approves, the comment will be made accessible in conjunction with the type registration.

Change Procedures Once a media type has been published by the IANA, the change controller may request a change to its definition. The same procedure that would be appropriate for the original registration request is used to process a change request. Media type registrations may not be deleted; media types that are no longer believed appropriate for use can be declared OBSOLETE by a change to their "intended use" field. Significant changes to a media type's definition should be requested only when there are serious omissions or errors in the published specification. When review is required, a change request may be denied if it renders entities that were valid under the previous definition invalid under the new definition. The change controller of a media type may pass responsibility to another person or agency by informing the IANA; this can be done without discussion or review. The IESG may reassign responsibility for a media type. The most common case of this will be to enable changes to be made to types where the author of the registration has died, fallen out of contact, or is otherwise unable to make changes that are important to the community.

Registration Template

Type name:

Subtype name:

Required parameters:

Optional parameters:

Encoding considerations:

Security considerations:

Interoperability considerations:

Published specification:

Applications that use this media type:

Fragment identifier considerations:

Additional information:

Deprecated alias names for this type: Magic number(s): File extension(s): Macintosh file type code(s):

Person & email address to contact for further information:

Intended usage:

(One of COMMON, LIMITED USE, or OBSOLETE.)

Restrictions on usage:

(Any restrictions on where the media type can be used go here.)

Author:

Change controller:

Provisional registration? (standards tree only):

Yes/No

(Any other information that the author deems interesting may be added below this line.) "N/A", written exactly that way, can be used in any field if desired to emphasize the fact that it does not apply or that the question was not omitted by accident. Do not use 'none' or other words that could be mistaken for a response. Limited-use media types should also note in the applications list whether or not that list is exhaustive.

Structured Syntax Suffix Registration Procedures Someone wishing to define a "+suffix" name for a structured syntax for use with a new media type registration SHOULD:

1. Check IANA's registry of media type name suffixes to see whether or not there is already an entry for that well-defined structured syntax.
2. If there is no entry for their suffix scheme, fill out the template (specified in ) and include that with the media type registration. The template may be contained in an Internet Draft, alone or as part of some other protocol specification. The template may also be submitted in some other form (as part of another document or as a stand-alone document), but the contents will be treated as an "IETF Contribution" under the guidelines of BCP 78 .
3. Send a copy of the template or a pointer to the containing document (with specific reference to the section with the template) to the mailing list media-types@iana.org, requesting review. This may be combined with a request to review the media type registration. Allow a reasonable time for discussion and comments.
4. Respond to review comments and make revisions to the proposed registration as needed to bring it into line with the guidelines given in this document.
5. Submit the (possibly updated) registration template (or pointer to the document containing it) to IANA at iana@iana.org.

Upon receipt of a structured syntax suffix registration request,

1. IANA checks the submission for completeness; if sections are missing or citations are not correct, IANA rejects the registration request.
2. IANA checks the current registry for an entry with the same name; if such a registry exists, IANA rejects the registration request.
3. IANA requests Expert Review of the registration request against the corresponding guidelines.
4. The Designated Expert may request additional review or discussion, as necessary.
5. If Expert Review recommends registration, IANA adds the registration to the appropriate registry.

The initial registry content specification provides examples of structured syntax suffix registrations.

Change Procedures Registrations may be updated in each registry by the same mechanism as required for an initial registration. In cases where the original definition of the scheme is contained in an IESG-approved document, update of the specification also requires IESG approval.

Structured Syntax Suffix Registration Template This template describes the fields that must be supplied in a structured syntax suffix registration request:

Name

Full name of the well-defined structured syntax.

+suffix

Suffix used to indicate conformance to the syntax.

References

Include full citations for all specifications necessary to understand the structured syntax.

Encoding considerations

A full citation to a section in a specification that provides general guidance regarding encoding considerations for any type employing this syntax. The same requirements for media type encoding considerations given in apply here.

Interoperability considerations

A full citation to a section in a specification that documents any issues regarding the interoperable use of types employing this structured syntax should be given here. Examples would include the existence of incompatible versions of the syntax, issues combining certain charsets with the syntax, or incompatibilities with other types or protocols.

Fragment identifier considerations

A full citation to a section in a specification that documents the generic processing rules of fragment identifiers for any type employing this syntax should be described here.

Security considerations

A full citation to a section in a specification that provides security considerations shared by media types employing this structured syntax must be specified here. The same requirements for media type security considerations given in apply here, with the exception that the option of not assessing the security considerations is not available for suffix registrations.

Contact

Person (including contact information) to contact for further information.

Author/Change controller.

Person (including contact information) authorized to change this suffix registration.

Security Considerations Security requirements for both media type and media type suffix registrations are discussed in .

IANA Considerations None Yet.

Acknowledgments The current authors would like to acknowledge their debt to the late Dr. Jon Postel, whose general model of IANA registration procedures and specific contributions shaped the predecessors of this document . We hope that the current version is one with which he would have agreed but, as it is impossible to verify that agreement, we have regretfully removed his name as a co-author. Randy Bush, Francis Dupont, Bjoern Hoehrmann, Barry Leiba, Murray Kucherawy, Alexey Melnikov, S. Moonesamy, Mark Nottingham, Tom Petch, Peter Saint-Andre, and Jeni Tennison provided many helpful review comments and suggestions.

References Normative References The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This initial document specifies the various headers used to describe the structure of MIME messages. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This specification standardizes three media types -- application/xml, application/xml-external-parsed-entity, and application/xml-dtd -- for use in exchanging network entities that are related to the Extensible Markup Language (XML) while defining text/xml and text/ xml-external-parsed-entity as aliases for the respective application/ types. This specification also standardizes the '+xml' suffix for naming media types outside of these five types when those media types represent XML MIME entities. The IETF policies about Intellectual Property Rights (IPR), such as patent rights, relative to technologies developed in the IETF are designed to ensure that IETF working groups and participants have as much information as possible about any IPR constraints on a technical proposal as early as possible in the development process. The policies are intended to benefit the Internet community and the public at large, while respecting the legitimate rights of IPR holders. This document sets out the IETF policies concerning IPR related to technology worked on within the IETF. It also describes the objectives that the policies are designed to meet. This document updates RFC 2026 and, with RFC 5378, replaces Section 10 of RFC 2026. This document also obsoletes RFCs 3979 and 4879. The IETF policies about rights in Contributions to the IETF are designed to ensure that such Contributions can be made available to the IETF and Internet communities while permitting the authors to retain as many rights as possible. This memo details the IETF policies on rights in Contributions to the IETF. It also describes the objectives that the policies are designed to meet. This memo obsoletes RFCs 3978 and 4748 and, with BCP 79 and RFC 5377, replaces Section 10 of RFC 2026. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies the procedure to register RTP payload formats as audio, video, or other media subtype names. This is useful in a text-based format description or control protocol to identify the type of an RTP transmission. [STANDARDS-TRACK] This second document defines the general structure of the MIME media typing system and defines an initial set of media types. [STANDARDS-TRACK] A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] Multipurpose Internet Mail Extensions (MIME) and various other Internet protocols are capable of using many different charsets. This in turn means that the ability to label different charsets is essential. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document changes RFC 2046 rules regarding default "charset" parameter values for "text/*" media types to better align with common usage by existing clients and servers. [STANDARDS-TRACK] ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279. Internet mail was originally limited to 7-bit ASCII. MIME added support for the use of 8-bit character sets in body parts, and also defined an encoded-word construct so other character sets could be used in certain header field values. However, full internationalization of electronic mail requires additional enhancements to allow the use of Unicode, including characters outside the ASCII repertoire, in mail addresses as well as direct use of Unicode in header fields like "From:", "To:", and "Subject:", without requiring the use of complex encoded-word constructs. This document specifies an enhancement to the Internet Message Format and to MIME that allows use of Unicode in mail addresses and most header field content. This specification updates Section 6.4 of RFC 2045 to eliminate the restriction prohibiting the use of non-identity content-transfer- encodings on subtypes of "message/". [STANDARDS-TRACK] Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. Historically, designers and implementers of application protocols have often distinguished between standardized and unstandardized parameters by prefixing the names of unstandardized parameters with the string "X-" or similar constructs. In practice, that convention causes more problems than it solves. Therefore, this document deprecates the convention for newly defined parameters with textual (as opposed to numerical) names in application protocols. This memo documents an Internet Best Current Practice. Informative References Apple Computer, Inc. MicroSoft Inc. This document defines procedures for the specification and registration of media types for use in MIME and other Internet protocols. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo defines extensions to the RFC 2045 media type and RFC 2183 disposition parameter value mechanisms. This memo also defines an extension to the encoded words defined in RFC 2047 to allow the specification of the language to be used for display as well as the character set. [STANDARDS-TRACK] By default, header field values in Hypertext Transfer Protocol (HTTP) messages cannot easily carry characters outside the US-ASCII coded character set. RFC 2231 defines an encoding mechanism for use in parameters inside Multipurpose Internet Mail Extensions (MIME) header field values. This document specifies an encoding suitable for use in HTTP header fields that is compatible with a simplified profile of the encoding defined in RFC 2231. This document obsoletes RFC 5987. Mitra The purpose of this memo is to propose an update to Internet RFC 2045 to include a new primary content-type to be known as "model". [STANDARDS-TRACK] This memo serves to register and document the "font" top-level media type, under which subtypes for representation formats for fonts may be registered. This document also serves as a registration application for a set of intended subtypes, which are representative of some existing subtypes already in use, and currently registered under the "application" tree by their separate registrations. This memo serves to register and document the 'haptics' top-level media type, under which subtypes for representation formats for haptics may be registered. This document also serves as a registration for a set of subtypes, which are representative of some existing subtypes already in use. This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. This memo documents the process used by the Internet community for the standardization of protocols and procedures. It defines the stages in the standardization process, the requirements for moving a document between stages and the types of documents used during this process. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A content media type name sometimes includes partitioned meta- information distinguished by a structured syntax to permit noting an attribute of the media as a suffix to the name. This document defines several structured syntax suffixes for use with media type registrations. In particular, it defines and registers the "+json", "+ber", "+der", "+fastinfoset", "+wbxml" and "+zip" structured syntax suffixes, and provides a media type structured syntax suffix registration form for the "+xml" structured syntax suffix. This document is not an Internet Standards Track specification; it is published for informational purposes. This set of documents, collectively called the Multipurpose Internet Mail Extensions, or MIME, redefines the format of messages. This fourth document, RFC 2048, specifies various IANA registration procedures for some MIME facilities. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.

Historical Note The media type registration process was initially defined for registering media types for use in the context of the asynchronous Internet mail environment. In this mail environment, there is a need to limit the number of possible media types, to increase the likelihood of interoperability when the capabilities of the remote mail system are not known. As media types are used in new environments in which the proliferation of media types is not a hindrance to interoperability, the original procedure proved excessively restrictive and had to be generalized. This was initially done in , but the procedure defined there was still part of the MIME document set. The media type specification and registration procedure is now a separate document, to make it clear that it is independent of MIME. It may be desirable to restrict the use of media types to specific environments or to prohibit their use in other environments. This specification incorporates such restrictions into media type registrations in a systematic way. See for additional discussion.

Grandfathered Media Types A number of media types with unfaceted subtype names, registered prior to 1996, would, if registered under the guidelines in this document, be given a faceted name and placed into either the vendor or personal trees. Reregistration of those types to reflect the appropriate trees is encouraged but not required. Ownership and change control principles outlined in this document apply to those types as if they had been registered in the trees described above. From time to time there may also be cases where a media type with an unfaceted subtype name has been widely deployed without being registered. (Note that this includes subtype names beginning with the "x-" prefix.) If possible, such a media type SHOULD be reregistered with a proper faceted subtype name, possibly using a deprecated alias to identify the original name (see ). However, if this is not possible, the type can, subject to approval by both the media types reviewer and the IESG, be registered in the proper tree with its unfaceted name.