Internet media type

A media type (also MIME type and content type) is a two-part identifier for file formats and format contents transmitted on the Internet. The Internet Assigned Numbers Authority (IANA) is the official authority for the standardization and publication of these classifications. Media types were originally defined in Request for Comments 2045 in November 1996 as a part of MIME (Multipurpose Internet Mail Extensions) specification, for denoting type of email message content and attachments; hence the name MIME type. It is also used by other internet protocols like HTTP and document file formats like HTML, for similar purpose.

A media type is composed of a type, a subtype, and optional parameters.

As an example, an HTML file might be designated text/html; charset=UTF-8. In this example text is the type, html is the subtype, and charset=UTF-8 is an optional parameter indicating the character encoding.

Media type consists of top-level type name and sub-type name, which is further structured into so-called "trees". Media types can optionally define companion data, known as parameters.

top-level type name / subtype name [ ; parameters ]

top-level type name / [ tree. ] subtype name [ +suffix ] [ ; parameters ]

The currently registered top-level type names are: application, audio, example, font, image, message, model, multipart, text, video.

An unofficial top-level name in common use is called chemical.

Sub-type name typically consists of a media type name, but it may or must also contain other content, such as tree prefix (facet), producer's name, product name or suffix - according to the different rules in registration trees.

All media types should be registered using the IANA registration procedures. For the efficiency and flexibility of the media type registration process, different structures of sub-type names can be registered in registration "trees" that are distinguished by the use of faceted names, e.g. sub-type names that begin with a "tree." prefix (facet). Currently the following trees are created: standard, vendor, personal or vanity, unregistered "x.". These registration trees were first defined in November 1996 (obsoleted RFC 2048 - currently RFC 6838). New registration trees may be created by IETF Standards Action - for external registration and management by well-known permanent organizations (e.g. scientific societies).

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