Documentation for HTTP:DEFINE-URL-EXPORT-TYPE

Top-level method for defining a new EXPORT-TYPE for a static, file-located data source.
FILE-EXTENSION is a keyword denoting the primary extension used  for the pathname type.
DATA-TYPE is a keyword that describes the type of resource.  The default is to use the
major mime type, but some cases will want to specialize it.  It can be any of :TEXT, :LISP,
:HTML ,:IMAGE, :AUDIO, :VIDEO, :WORLD, or :APPLICATION. 
MIME-CONTENT-TYPE is a keyword list of (major-type subtype).
COPY-MODE is either :TEXT, :BINARY, or :CRLF.
ALTERNATE-EXTENSIONS is an optional list of keywords denoting alternative extensions used for
the pathname type.
Automatic definition of methods can be suppessed with NO-METHODS, which is a list 
and accepts values :EXPORT, :HEADER, :DOCUMENT.