MIME types are used in many applications, for instance as part of e-mail
and HTTP traffic, to indicate the type of content that is transmitted.
Sometimes detailed knowledge about a mime-type is need; however, this
module only knows about the file-name extensions that relate to some
file-type. It can also be used to produce the right format: types that
are not registered at IANA need to use 'x-' prefixes.
