(published in RFC 3023 in January 2001, last updated 2014-04-17 
via RFC7303)

Type name:  application

Subtype name:  xml-dtd

Required parameters:  none

Optional parameters:  charset

   See Section 3 of RFC7303.

Encoding considerations:  Same as for application/xml (Section 9.1 
   of RFC7303).

Security considerations:  See Section 10 of RFC7303.

Interoperability considerations:  XML DTDs have proven to be
   interoperable by DTD authoring tools and XML validators, among
   others.

Published specification:  Same as for application/xml (Section 9.1 
   of RFC7303).

Applications which use this media type:  DTD authoring tools handle
   external DTD subsets as well as external parameter entities.  XML
   validators may also access external DTD subsets and external
   parameter entities.

Additional information:

   Magic number(s):  Same as for application/xml (Section 9.1 of 
   RFC7303).

   File extension(s):  .dtd or .mod

   Macintosh File Type Code(s):  "TEXT"

Person and email address for further information:  See Authors'
   Addresses section in RFC7303.

Intended usage:  COMMON

Author:  See Authors' Addresses section in RFC7303.

Change controller:  The XML specification is a work product of the
   World Wide Web Consortium's XML Core Working Group.  The W3C has
   change control over RFC7303.