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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 (including but not limited to HTTP and MIME ) are capable of carrying arbitrary labeled content. Those labels are known as media types. A media type consists of a top-level type () and a subtype (), which is further structured into a tree (identified by a prefix). A subtype can also be associated with a structured syntax (identified by suffix). Optionally, a media type can be defined to allow companion data, known as parameters. defines the criteria for registering media types. outlines the procedures used to do so. The location of the media type registry is:

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

outlines the procedures for managing the registry for structured syntax suffixes. It is located at:

• https://www.iana.org/assignments/media-type-structured-suffix/

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 (). 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. 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.

Specification 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 needs 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 needs to be referenced by it. A specification need not be publicly available for media types registered in the vendor and personal trees. Note, however, that the public availability of a specification will often make the difference between having a name reserved and having the potential for useful interoperation.

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. Copyright on the registration template needs to allow the IANA to copy it into the IANA registry.

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 type and subtype 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 using multiple names prior to registration. In such cases, a preferred name MUST be chosen for the media type, and applications are required to use this to be compliant with the type's registration. However, a list of deprecated aliases by which the type is known can be supplied as additional information in order to assist applications in processing the media type properly.

Parameters Media types can 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 are required to 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 needs to 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. Some parameters are reused across multiple media type definitions to provide common functionality. For example, the 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types identify media codecs used inside the container and their parameters. RTP payload formats have several common parameters: see , and . 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 can 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. An "encoding considerations" field is provided to note what sort of data a media type can consist of as part of its registration. 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 limited to knowledge of the boundaries between successive frames and knowledge of the transport mechanism. Note that media types of this sort cannot be stored in a file or transported as a stream of octets without further context; therefore, such media types are thus 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 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 need to 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 can 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 need to 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 can be extended by use of the "comments on media types" mechanism described in below. Issues that need to be described in a security analysis of a media type include:

• 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.

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 can 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 specification itself.

Non-Requirements Universal support and implementation of a media type are NOT a requirement for registration. In some environments such as mail, information on the capabilities of the remote mail agent is frequently not available to the sender. When this is the case, maximum interoperability might be attained by restricting the media types used to those "common" formats expected to be widely implemented. In the past, this reasoning was used 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 that environment. A media type intended for limited use should note this in its registration. The "Restrictions on Usage" field is provided for this purpose.

Top-Level Media Types The list of top-level types is maintained in the IANA Top-Level Media Types registry at:

• https://www.iana.org/assignments/top-level-media-types/

Top-level types can place various restrictions on the media types that use them. New media types MUST conform to the restrictions (if any) of their top-level type.

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 top-level type can be defined to accommodate it. Registration of a new top-level type requires Standards Action in the IETF and, hence, the publication of a RFC on the Standards Track.

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

• The top-level type is defined in a Standards Track RFC (see ). This will make sure there is sufficient community interest, review, and consensus.
• The IANA Considerations section of that RFC requests 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 are defined clearly. This will help the Designated Expert(s) 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.
• The RFC clearly documents security considerations applying to all or a significant subset of subtypes.
• At the minimum, one subtype is 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 definition 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:

• Media types are not a general type system. A top-level type whose main or only purpose is to map other type systems, protocol elements, or registration spaces is not appropriate. Examples of such discouraged uses include mapping media types to programming language primitives, ontologies, object identifiers, URIs and URI schemes, and file extensions. That said, media types can use parameters to carry such information. For example, information on a file extension '.dcat' can be encoded as 'application/octet-string; filename=foo.dcat'.
• 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 ought not be used. See .

Media Subtypes

Registration Trees To increase the efficiency and flexibility of the registration process, different structures of subtype names can be registered in "trees," distinguished with faceted prefixes. 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 subtype name would begin with a "vnd." prefix. Note that some previously defined media types do not conform to the naming conventions described below; see .

Standards Tree The standards tree is intended for those media types that require a substantive review and approval process in a recognized standards-related organization. For media types that do not require such a process, see the vendor and personal trees. Registrations in the standards tree are either:

1. 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 on the IETF stream, and can be used for RFCs from other streams. In the second case, the IESG makes a one-time decision on whether the registration submitter represents a recognized standards-related organization; after that, registration requests are performed as specified in . The format is required to be described by a formal specification produced by the submitting standards-related organization. The third case is described in . Media types registered by the IETF in the standards tree MUST be published as RFCs. Standards-tree registrations for media types defined by other standards-related organizations MUST be described by a formal specification produced by that organization. Note that in both cases, the early allocation process described in is available. Media types in the standards tree do not have faceted subtype names, unless they are given legacy status 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. In the case of IETF standards, the change controller is normally the IESG. 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.

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 media type 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. The intent is to assure that successfully deployed community formats have registered media types. As such, the criteria above are designed to preclude anticipatory registrations. Note that such registrations still go through preliminary community review (), and decisions can be appealed ().

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. A registration may be placed in the vendor tree by anyone who needs to interchange data 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 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@ietf.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@ietf.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 subtype 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-" subtype name prefix, it can be registered in an alternative tree by following the procedure defined in .

Additional Registration Trees New top-level registration trees may be created by IETF Standards Action. It is explicitly assumed that these trees might be created for external registration and management by well-known permanent organizations; for example, scientific societies might 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.

Structured Syntax Suffixes Media types can be identified as using a well-known structured syntax (for example, XML or JSON) using use a "+suffix" convention. A structured syntax 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 syntax suffix MUST NOT contain more than one "+" sign. For example, in the "application/foo+bar" media type "application" is the top-level type, "foo" is the subtype name, and "+bar" is the structured syntax suffix. A media type such as "application/foo+bar+baz" is not registrable. Structured syntax suffixes are required to be registered before use by a media type registration; see . Media types that make use of a structured syntax SHOULD use the appropriate suffix, and MUST NOT use suffixes for structured syntaxes that they do not actually employ. Media types that make use of a structured syntax, or similar separator such as a dash "-", SHOULD be semantically aligned, from a data model perspective, with existing 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 subtype name "application/foo" are the same between both media types. Registrations are expected to align with existing subtype or suffix names in the media type registry. A registration request for a media type that uses an existing subtype or suffix is expected to be coordinated with the change controller for the already registered media type.

Use Cases for Structured Syntax Suffixes Common use cases for media types that employ structured syntax suffixes include:

• Identifying use of a structured data format; for example "+xml", "+json", "+yaml", and "+cbor"
• Flagging compression with a format such as "+zip" or "+gzip"
• Flagging encoding in a digital signature format such as "+jwt" or "+cose"

While it might be desirable to indicate multiple use cases simultaneously using a compound suffix (e.g., "+xml+zip"), experience shows that suffixes are a poor basis for this; the combinations of suffixes quickly multiply, and there is not a well-specified processing model that can handle them safely. Therefore, multiple suffixes are disallowed from use.

Fragment Identifiers and Structured Syntax Suffixes Structured syntax suffixes are able to specify fragment identifier handling for all subtypes that utilise them, as indicated in the "Fragment Identifier Considerations" column of the Structured Syntax Suffixes registry. Individual subtypes can specify additional handling. To ensure consistent processing, precedence is determined by the following rules (first match winning):

1. When the structured syntax suffix defines fragment identifier handling and it successfully resolves the fragment identifier, that determines fragment identifier handling;
2. Otherwise, the specific media type determines fragment identifier handling.

Security Considerations for Structured Syntax Suffix Processing Processors that utilise the information in structured syntax suffixes encounter the following security considerations.

Relationships Between Types The relationship between a media type that employs a structured syntax suffix and the type (if any) that results from removing that suffix cannot be known merely by examining the types. For example, content marked "application/foo+bar" may or may not be processable or valid as "application/foo" content. It may be possible to derive one from the other, but that is specific to the structured syntax suffix and/or media type itself. This uncertainty extends to fragment identifier processing: per the rules in , a fragment identifier that might be valid for an "application/foo+bar" document might not be applicable to another "+bar" document, because media-type specific fragment identifier resolution might be used. Likewise, the security characteristics that a processor needs to consider may change depending upon whether it is solely processing the structured syntax suffix or the entire media type. For example, a processor cannot presume that the security characteristics for a "+bar" document will be the same as for a "application/foo+bar" document.

Partial Processing An attacker might append structured syntax suffixes in order to trick processors into skipping security checks. For example, an attacker might use an "application/vnd.ms-excel.addin.macroEnabled.12+zip" structured syntax suffix to trigger an unzip process into invoking Microsoft Excel, bypassing anti-virus scanners that would normally block the file from being opened. Enterprising attackers might take advantage of toolchains that partially process media types in this manner. Processing of media types based only on the presence of a structured syntax suffix needs to ensure that further processing does not blindly trust the decoded data. For example, proper magic header or file structure checking could mitigate this attack.

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@ietf.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@ietf.org mailing list for review. Registrations in other trees can 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 are 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:

• https://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 can 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 can 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 Designated Expert(s), who are appointed by the IETF Applications Area Director(s). Designated Expert(s) examine registration requests to make sure they meet the requirements set forth in this document. Decisions made by the Designated Expert(s) 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 needs to 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 Designated Expert(s) 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 Designated Expert(s), 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. When a change to a media type registration is requested, the Designated Expert(s) will assure that the change controller approves the change. If the Designated Expert(s) find that the change controller is unresponsive or uncontactable for a reasonable period of time and reasonable efforts have been made to contact the change controller, they may recommend to the IESG that the change controller be updated. The IESG makes the final decision regarding updates to change controllers.

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 Structured syntax suffixes must be described by a readily available description, preferably within a document published by an established standards-related organization, for which there's a reference that can be used in a Normative References section of an RFC. 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@ietf.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

Top-Level Types Registry In the Top-Level Media Types registry, IANA should link the reference field for each top-level type to the specific subsection in question, rather than just the relevant RFC.

Recognized Standards Organisations IANA should notify recognized standards organisations when this document is published (where feasible), and highlight the need to consider how their processes interact with the registration proceedure (see eg https://www.w3.org/guide/editor/mediatypes.html#registration-process).

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.

Contributors Much of the text of this document is directly taken from and . We acknowledge the following authors of those documents as contributors to this: Ned Freed John C. Klensin 1770 Massachusetts Ave, #322 Cambridge, MA 02140 USA EMail: john+ietf@jck.com Tony Hansen AT&T Laboratories 200 Laurel Ave. Middletown, NJ 07748 USA EMail: tony+mtsuffix@maillennium.att.com Martin J. Dürst Aoyama Gakuin University Fuchinobe 5-10-1, Chuo-ku, Sagamihara, Kanagawa 252-5258 Japan Phone: +81 42 759 6329 Email: duerst@it.aoyama.ac.jp URI: https://www.sw.it.aoyama.ac.jp/Dürst/

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] 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. This memo describes the process for early allocation of code points by IANA from registries for which "Specification Required", "RFC Required", "IETF Review", or "Standards Action" policies apply. This process can be used to alleviate the problem where code point allocation is needed to facilitate desired or required implementation and deployment experience prior to publication of an RFC, which would normally trigger code point allocation. The procedures in this document are intended to apply only to IETF Stream documents. 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] Several MIME type/subtype combinations exist that can contain different media formats. A receiving agent thus needs to examine the details of such media content to determine if the specific elements can be rendered given an available set of codecs. Especially when the end system has limited resources, or the connection to the end system has limited bandwidth, it is helpful to know from the Content- Type alone if the content can be rendered. This document specifies two parameters, 'codecs' and 'profiles', that are used with various MIME types or type/subtype combinations to allow for unambiguous specification of the codecs employed by the media formats contained within, or the profile(s) of the overall container format. This document obsoletes RFC 4281; RFC 4281 defines the 'codecs' parameter, which this document retains in a backwards compatible manner with minor clarifications; the 'profiles' parameter is added by this document. By labeling content with the specific codecs indicated to render the contained media, receiving systems can determine if the codecs are supported by the end system, and if not, can take appropriate action (such as rejecting the content, sending notification of the situation, transcoding the content to a supported type, fetching and installing the required codecs, further inspection to determine if it will be sufficient to support a subset of the indicated codecs, etc.). Similarly, the profiles can provide an overall indication, to the receiver, of the specifications with which the content complies. This is an indication of the compatibility of the container format and its contents to some specification. The receiver may be able to work out the extent to which it can handle and render the content by examining to see which of the declared profiles it supports, and what they mean. [STANDARDS-TRACK] In this specification, we define a framework for specifying restrictions on RTP streams in the Session Description Protocol (SDP). This framework defines a new "rid" ("restriction identifier") SDP attribute to unambiguously identify the RTP streams within an RTP session and restrict the streams' payload format parameters in a codec-agnostic way beyond what is provided with the regular payload types. This specification updates RFC 4855 to give additional guidance on choice of Format Parameter (fmtp) names and their relation to the restrictions defined by this document. 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 registers and documents 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 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. 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 document defines best practices for defining new top-level media types. It also introduces a registry for top-level media types, and contains a short history of top-level media types. It updates RFC 6838.

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.

Legacy Media Types Some media types registered prior to 1996 with unfaceted subtype names, 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 those trees. There may also be cases where a media type with an unfaceted subtype name has been widely deployed without being registered. In these cases, the community format registration process () ought be considered.