function readPrecedingKeyword(pos, match) {
  if (pos < match.length - 1) return false;
  return (
    source.startsWith(match, pos - match.length + 1) &&
    (pos === 0 ||
      isBrOrWsOrPunctuatorNotDot(source.charCodeAt(pos - match.length)))
  );
}
@param {number} pos
@param {string} match