code: def regex_opt(strings, prefix='', suffix=''):
      
      strings = sorted(strings)
      return prefix + regex_opt_inner(strings, '(') + suffix
docs: Return a compiled regex that matches any string in the given list.
  
      The strings to match must be literal strings, not regexes.  They will be
      regex-escaped.
  
      *prefix* and *suffix* are pre- and appended to the final regex.