DuckCorp Dico

Found one definition

1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   Rx
      A pattern matcher compatible with GNU regex, but generally
      faster.
      Version 0.05, released 1994-05-18, contained substantial
      changes from the version last distributed with GNU sed.
      These changes provide low-level support for searching across
      arbitrarily fragmented strings and suspendable searches.