          unknown cmdName ?arg arg ...?
               This command doesn't actually exist as part of Tcl, but
               Tcl will invoke it  if  it  does  exist.   If  the  Tcl
               interpreter  encounters  a command name for which there
               is not a defined  command,  then  Tcl  checks  for  the
               existence  of  a command named unknown.  If there is no
               such command, then the interpeter returns an error.  If
               the  unknown  command  exists,  then it is invoked with
               arguments consisting of the fully-substituted name  and
               arguments  for  the original non-existent command.  The
               unknown command typically does  things  like  searching
               through  library  directories  for  a command procedure
               with the name cmdName, or expanding abbreviated command
               names   to   full-length,  or  automatically  executing
               unknown commands as UNIX sub-processes.  In some  cases
               (such  as  expanding abbreviations) unknown will change
               the original command slightly and then (re-)execute it.
               The result of the unknown command is used as the result
               for the original non-existent command.
