ion 'rl_completion_matches()' uses an
     application-supplied "generator" function to generate the list of
     possible matches, and then returns the array of these matches.  The
     caller should place the address of its generator function in
     'rl_completion_entry_function'.

  3. The generator function is called repeatedly from
     'rl_completion_matches()', returning a string each time.  The
     arguments to the generator function are TEXT and STATE.  TEXT is
     the partial word to be completed.  STATE is zero the first time the
     function is called, allowing the generator to perform any necessary
     initialization, and a positive non-zero integer for each subsequent
     call.  The generator function returns '(char *)NULL' to inform
     'rl_completion_matches()' that there are no more possibilities
     left.  Usually the generator function computes the list of possible
     completions when STATE is zero, and returns them one at a time on
     subsequent calls.  Each string the generator function returns as a
     match must be allocated with 'malloc()'; Readline frees the strings
     when it has finished with them.  Such a generator function is
     referred to as an "application-specific completion function".

 -- Function: int rl_complete (int ignore, int invoking_key)
     Complete the word at or before point.  You have supplied the
     function that does the initial simple matching selection algorithm
     (see 'rl_completion_matches()').  The default is to do filename
     completion.

 -- Variable: rl_compentry_func_t * rl_completion_entry_function
     This is a pointer to the generator function for
     'rl_completion_matches()'.  If the value of
     'rl_completion_entry_function' is 'NULL' then the default filename
     generator function, 'rl_filename_completion_function()', is used.
     An "application-specific completion function" is a function whose
     address is assigned to 'rl_completion_entry_function' and whose
     return values are used to generate possible completions.