HTTP uses Internet Media Types [13] in the Content-Type header field (Section 10.5) in order to provide open and extensible data typing.
media-type = type "/" subtype *( ";" parameter )
type = token
subtype = token
Parameters may follow the type/subtype in the form of attribute/value pairs.
parameter = attribute "=" value
attribute = token
value = token | quoted-string
The type, subtype, and parameter attribute names are case- insensitive. Parameter values may or may not be case-sensitive, depending on the semantics of the parameter name. LWS must not be generated between the type and subtype, nor between an attribute and its value. Upon receipt of a media type with an unrecognized parameter, a user agent should treat the media type as if the unrecognized parameter and its value were not present.
Some older HTTP applications do not recognize media type parameters. HTTP/1.0 applications should only use media type parameters when they are necessary to define the content of a message.
Media-type values are registered with the Internet Assigned Number Authority (IANA [15]). The media type registration process is outlined in RFC 1590 [13]. Use of non-registered media types is discouraged.