docs: def best_guess(self, line, args=None, kwargs=None, multiple=True, **options):
          """\
          Given multiple=False, this will simply return the first matching
          regexes first handler; otherwise, this will return a list of all
          the matching handler function(s).
  
          If rank_best was set on the parser, this will attempt to "rank" the
          regexes, and will return the highest ranked handler(s).
  
          Returns (matches, args, kwargs) - it's up to the caller to apply these
          and test whether f.options["inject"]/f.no_args is set, etc.
          """
          cmd, _args, _kwargs = self.parse(line)
          if args is None:
              args = _args
          if kwargs is None:
              kwargs = _kwargs
          matches = []
          for regex, funcs in self.handlers.items():
              if not regex.findall(cmd):
                  continue
              if not multiple:
                  return ((funcs[0], args, kwargs)
                           if len(funcs) > 0
                           else (None, args, kwargs))
              matches.append(funcs)
          if self.rank_best:
              # TODO: rank regexes.
              pass
          return (matches, args, kwargs)