On the following pages are descriptions of each command recognized by
   the NNTP server and the responses which will be returned by those
   commands.

   Each command is shown in upper case for clarity, although case is
   ignored in the interpretation of commands by the NNTP server.  Any
   parameters are shown in lower case.  A parameter shown in [square
   brackets] is optional.  For example, [GMT] indicates that the
   triglyph GMT may present or omitted.

   Every command described in this section must be implemented by all
   NNTP servers.

   There is no prohibition against additional commands being added;
   however, it is recommended that any such unspecified command begin
   with the letter "X" to avoid conflict with later revisions of this
   specification.

   Implementors are reminded that such additional commands may not
   redefine specified status response codes.  Using additional
   unspecified responses for standard commands is also prohibited.