Concept
A media type (formerly known as a MIME type) is a two-part identifier for file formats and format contents transmitted on the Internet. Their purpose is somewhat similar to file extensions in that they identify the intended data format. 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 (MIME) Part One: Format of Internet Message Bodies (Nov 1996) in November 1996 as a part of the MIME (Multipurpose Internet Mail Extensions) specification, for denoting type of email message content and attachments; hence the original name, MIME type. Media types are also used by other internet protocols such as HTTP and document file formats such as HTML, for similar purposes. A media type consists of a type and a subtype, which is further structured into a tree. A media type can optionally define a suffix and parameters: As an example, an HTML file might be designated . In this example, is the type, is the subtype, and is an optional parameter indicating the character encoding. Types, subtypes, and parameter names are case-insensitive. Parameter values are usually case-sensitive, but may be interpreted in a case-insensitive fashion depending on the intended use. The "type" part defines the broad use of the media type. As of November 1996, the registered types were: , , , , , and . By December 2020, the registered types included the foregoing, plus , , and . An unofficial top-level type in common use is . A subtype typically consists of a media format, but it may or must also contain other content, such as a tree prefix, producer, product 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 subtypes can be registered in registration trees that are distinguished by the use of tree prefixes.