code: def strongest_match(cls, overlay, mode, backend=None):
          
          match_strength = [(op.match_level(overlay), op) for op in cls.definitions
                            if op.mode == mode and (not op.backends or backend in op.backends)]
          matches = [(match[0], op, match[1]) for (match, op) in match_strength if match is not None]
          if matches == []: return None
          else:             return sorted(matches)[0]
docs: Returns the single strongest matching compositor operation
          given an overlay. If no matches are found, None is returned.
  
          The best match is defined as the compositor operation with the
          highest match value as returned by the match_level method.