Getters for the static properties lastMatch, lastParen, leftContext, and rightContext of the RegExp constructor.  The properties are computed based on the captures array of the last successful match and the subject string of the last successful match.
function RegExpGetLastMatch() {
  var regExpSubject = LAST_SUBJECT(RegExpLastMatchInfo);
  return %_SubString(regExpSubject,
                     RegExpLastMatchInfo[CAPTURE0],
                     RegExpLastMatchInfo[CAPTURE1]);
}