code: function isIdentifierStart(ch) {
    return (ch === 0x24) || (ch === 0x5F) || // $ (dollar) and _ (underscore)
      (ch >= 0x41 && ch <= 0x5A) || // A..Z
      (ch >= 0x61 && ch <= 0x7A) || // a..z
      (ch === 0x5C) || // \ (backslash)
      ((ch >= 0x80) && RegexNonAsciiIdentifierStart.test(String.fromCharCode(ch)));
  }
docs: 7.6 Identifier Names and Identifiers