// regjsparser
//
// ==================================================================
//
// See ECMA-262 Standard: 15.10.1
//
// NOTE: The ECMA-262 standard uses the term "Assertion" for /^/. Here the
//   term "Anchor" is used.
//
// Pattern ::
//      Disjunction
//
// Disjunction ::
//      Alternative
//      Alternative | Disjunction
//
// Alternative ::
//      [empty]
//      Alternative Term
//
// Term ::
//      Anchor
//      Atom
//      Atom Quantifier
//
// Anchor ::
//      ^
//      $
//      \ b
//      \ B
//      ( ? = Disjunction )
//      ( ? ! Disjunction )
//      ( ? < = Disjunction )
//      ( ? < ! Disjunction )
//
// Quantifier ::
//      QuantifierPrefix
//      QuantifierPrefix ?
//
// QuantifierPrefix ::
//      *
//      +
//      ?
//      { DecimalDigits }
//      { DecimalDigits , }
//      { DecimalDigits , DecimalDigits }
//
// Atom ::
//      PatternCharacter
//      .
//      \ AtomEscape
//      CharacterClass
//      ( GroupSpecifier Disjunction )
//      ( ? : Disjunction )
//
// PatternCharacter ::
//      SourceCharacter but not any of: ^ $ \ . * + ? ( ) [ ] { } |
//
// AtomEscape ::
//      DecimalEscape
//      CharacterClassEscape
//      CharacterEscape
//      k GroupName
//
// CharacterEscape[U] ::
//      ControlEscape
//      c ControlLetter
//      HexEscapeSequence
//      RegExpUnicodeEscapeSequence[?U] (ES6)
//      IdentityEscape[?U]
//
// ControlEscape ::
//      one of f n r t v
// ControlLetter ::
//      one of
//          a b c d e f g h i j k l m n o p q r s t u v w x y z
//          A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
//
// IdentityEscape ::
//      SourceCharacter but not c
//
// DecimalEscape ::
//      DecimalIntegerLiteral [lookahead ∉ DecimalDigit]
//
// CharacterClassEscape ::
//      one of d D s S w W
//
// CharacterClass ::
//      [ [lookahead ∉ {^}] ClassRanges ]
//      [ ^ ClassRanges ]
//
// ClassRanges ::
//      [empty]
//      [~V] NonemptyClassRanges
//      [+V] ClassContents
//
// NonemptyClassRanges ::
//      ClassAtom
//      ClassAtom NonemptyClassRangesNoDash
//      ClassAtom - ClassAtom ClassRanges
//
// NonemptyClassRangesNoDash ::
//      ClassAtom
//      ClassAtomNoDash NonemptyClassRangesNoDash
//      ClassAtomNoDash - ClassAtom ClassRanges
//
// ClassAtom ::
//      -
//      ClassAtomNoDash
//
// ClassAtomNoDash ::
//      SourceCharacter but not one of \ or ] or -
//      \ ClassEscape
//
// ClassEscape ::
//      DecimalEscape
//      b
//      CharacterEscape
//      CharacterClassEscape
//
// GroupSpecifier ::
//      [empty]
//      ? GroupName
//
// GroupName ::
//      < RegExpIdentifierName >
//
// RegExpIdentifierName ::
//      RegExpIdentifierStart
//      RegExpIdentifierName RegExpIdentifierContinue
//
// RegExpIdentifierStart ::
//      UnicodeIDStart
//      $
//      _
//      \ RegExpUnicodeEscapeSequence
//
// RegExpIdentifierContinue ::
//      UnicodeIDContinue
//      $
//      _
//      \ RegExpUnicodeEscapeSequence
//      <ZWNJ>
//      <ZWJ>
//
// --------------------------------------------------------------
// NOTE: The following productions refer to the "set notation and
//       properties of strings" proposal.
//       https://github.com/tc39/proposal-regexp-set-notation
// --------------------------------------------------------------
//
// ClassContents ::
//      ClassUnion
//      ClassIntersection
//      ClassSubtraction
//
// ClassUnion ::
//      ClassRange ClassUnion?
//      ClassOperand ClassUnion?
//
// ClassIntersection ::
//      ClassOperand && [lookahead ≠ &] ClassOperand
//      ClassIntersection && [lookahead ≠ &] ClassOperand
//
// ClassSubtraction ::
//      ClassOperand -- ClassOperand
//      ClassSubtraction -- ClassOperand
//
// ClassOperand ::
//      ClassCharacter
//      ClassStrings
//      NestedClass
//
// NestedClass ::
//      [ [lookahead ≠ ^] ClassRanges[+U,+V] ]
//      [ ^ ClassRanges[+U,+V] ]
//      \ CharacterClassEscape[+U, +V]
//
// ClassRange ::
//      ClassCharacter - ClassCharacter
//
// ClassCharacter ::
//      [lookahead ∉ ClassReservedDouble] SourceCharacter but not ClassSyntaxCharacter
//      \ CharacterEscape[+U]
//      \ ClassHalfOfDouble
//      \ b
//
// ClassSyntaxCharacter ::
//      one of ( ) [ ] { } / - \ |
//
// ClassStrings ::
//      ( ClassString MoreClassStrings? )
//
// MoreClassStrings ::
//      | ClassString MoreClassStrings?
//
// ClassString ::
//      [empty]
//      NonEmptyClassString
//
// NonEmptyClassString ::
//      ClassCharacter NonEmptyClassString?
//
// ClassReservedDouble ::
//      one of && !! ## $$ %% ** ++ ,, .. :: ;; << == >> ?? @@ ^^ __ `` ~~
//
// ClassHalfOfDouble ::
//      one of & - ! # % , : ; < = > @ _ ` ~
//

(function() {

  var fromCodePoint = String.fromCodePoint || (function() {
    // Implementation taken from
    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint

    var stringFromCharCode = String.fromCharCode;
    var floor = Math.floor;

    return function fromCodePoint() {
      var MAX_SIZE = 0x4000;
      var codeUnits = [];
      var highSurrogate;
      var lowSurrogate;
      var index = -1;
      var length = arguments.length;
      if (!length) {
        return '';
      }
      var result = '';
      while (++index < length) {
        var codePoint = Number(arguments[index]);
        if (
          !isFinite(codePoint) ||       // `NaN`, `+Infinity`, or `-Infinity`
          codePoint < 0 ||              // not a valid Unicode code point
          codePoint > 0x10FFFF ||       // not a valid Unicode code point
          floor(codePoint) != codePoint // not an integer
        ) {
          throw RangeError('Invalid code point: ' + codePoint);
        }
        if (codePoint <= 0xFFFF) { // BMP code point
          codeUnits.push(codePoint);
        } else { // Astral code point; split in surrogate halves
          // http://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
          codePoint -= 0x10000;
          highSurrogate = (codePoint >> 10) + 0xD800;
          lowSurrogate = (codePoint % 0x400) + 0xDC00;
          codeUnits.push(highSurrogate, lowSurrogate);
        }
        if (index + 1 == length || codeUnits.length > MAX_SIZE) {
          result += stringFromCharCode.apply(null, codeUnits);
          codeUnits.length = 0;
        }
      }
      return result;
    };
  }());

  function parse(str, flags, features) {
    if (!features) {
      features = {};
    }
    function addRaw(node) {
      node.raw = str.substring(node.range[0], node.range[1]);
      return node;
    }

    function updateRawStart(node, start) {
      node.range[0] = start;
      return addRaw(node);
    }

    function createAnchor(kind, rawLength) {
      return addRaw({
        type: 'anchor',
        kind: kind,
        range: [
          pos - rawLength,
          pos
        ]
      });
    }

    function createValue(kind, codePoint, from, to) {
      return addRaw({
        type: 'value',
        kind: kind,
        codePoint: codePoint,
        range: [from, to]
      });
    }

    function createEscaped(kind, codePoint, value, fromOffset) {
      fromOffset = fromOffset || 0;
      return createValue(kind, codePoint, pos - (value.length + fromOffset), pos);
    }

    function createCharacter(matches) {
      var _char = matches[0];
      var first = _char.charCodeAt(0);
      if (hasUnicodeFlag) {
        var second;
        if (_char.length === 1 && first >= 0xD800 && first <= 0xDBFF) {
          second = lookahead().charCodeAt(0);
          if (second >= 0xDC00 && second <= 0xDFFF) {
            // Unicode surrogate pair
            pos++;
            return createValue(
                'symbol',
                (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000,
                pos - 2, pos);
          }
        }
      }
      return createValue('symbol', first, pos - 1, pos);
    }

    function createDisjunction(alternatives, from, to) {
      return addRaw({
        type: 'disjunction',
        body: alternatives,
        range: [
          from,
          to
        ]
      });
    }

    function createDot() {
      return addRaw({
        type: 'dot',
        range: [
          pos - 1,
          pos
        ]
      });
    }

    function createCharacterClassEscape(value) {
      return addRaw({
        type: 'characterClassEscape',
        value: value,
        range: [
          pos - 2,
          pos
        ]
      });
    }

    function createReference(matchIndex) {
      return addRaw({
        type: 'reference',
        matchIndex: parseInt(matchIndex, 10),
        range: [
          pos - 1 - matchIndex.length,
          pos
        ]
      });
    }

    function createNamedReference(name) {
      return addRaw({
        type: 'reference',
        name: name,
        range: [
          name.range[0] - 3,
          pos
        ]
      });
    }

    function createGroup(behavior, disjunction, from, to) {
      return addRaw({
        type: 'group',
        behavior: behavior,
        body: disjunction,
        range: [
          from,
          to
        ]
      });
    }

    function createQuantifier(min, max, from, to) {
      if (to == null) {
        from = pos - 1;
        to = pos;
      }

      return addRaw({
        type: 'quantifier',
        min: min,
        max: max,
        greedy: true,
        body: null, // set later on
        range: [
          from,
          to
        ]
      });
    }

    function createAlternative(terms, from, to) {
      return addRaw({
        type: 'alternative',
        body: terms,
        range: [
          from,
          to
        ]
      });
    }

    function createCharacterClass(contents, negative, from, to) {
      return addRaw({
        type: 'characterClass',
        kind: contents.kind,
        body: contents.body,
        negative: negative,
        range: [
          from,
          to
        ]
      });
    }

    function createClassRange(min, max, from, to) {
      // See 15.10.2.15:
      if (min.codePoint > max.codePoint) {
        bail('invalid range in character class', min.raw + '-' + max.raw, from, to);
      }

      return addRaw({
        type: 'characterClassRange',
        min: min,
        max: max,
        range: [
          from,
          to
        ]
      });
    }

    function createClassStrings(strings, from, to) {
      return addRaw({
        type: 'classStrings',
        strings: strings,
        range: [from, to]
      });
    }

    function createClassString(characters, from, to) {
      return addRaw({
        type: 'classString',
        characters: characters,
        range: [from, to]
      });
    }

    function flattenBody(body) {
      if (body.type === 'alternative') {
        return body.body;
      } else {
        return [body];
      }
    }

    function incr(amount) {
      amount = (amount || 1);
      var res = str.substring(pos, pos + amount);
      pos += (amount || 1);
      return res;
    }

    function skip(value) {
      if (!match(value)) {
        bail('character', value);
      }
    }

    function match(value) {
      if (str.indexOf(value, pos) === pos) {
        return incr(value.length);
      }
    }

    function lookahead() {
      return str[pos];
    }

    function current(value) {
      return str.indexOf(value, pos) === pos;
    }

    function next(value) {
      return str[pos + 1] === value;
    }

    function matchReg(regExp) {
      var subStr = str.substring(pos);
      var res = subStr.match(regExp);
      if (res) {
        res.range = [];
        res.range[0] = pos;
        incr(res[0].length);
        res.range[1] = pos;
      }
      return res;
    }

    function parseDisjunction() {
      // Disjunction ::
      //      Alternative
      //      Alternative | Disjunction
      var res = [], from = pos;
      res.push(parseAlternative());

      while (match('|')) {
        res.push(parseAlternative());
      }

      if (res.length === 1) {
        return res[0];
      }

      return createDisjunction(res, from, pos);
    }

    function parseAlternative() {
      var res = [], from = pos;
      var term;

      // Alternative ::
      //      [empty]
      //      Alternative Term
      while (term = parseTerm()) {
        res.push(term);
      }

      if (res.length === 1) {
        return res[0];
      }

      return createAlternative(res, from, pos);
    }

    function parseTerm() {
      // Term ::
      //      Anchor
      //      Atom
      //      Atom Quantifier

      if (pos >= str.length || current('|') || current(')')) {
        return null; /* Means: The term is empty */
      }

      var anchor = parseAnchor();

      if (anchor) {
        return anchor;
      }

      var atom = parseAtomAndExtendedAtom();
      if (!atom) {
        // Check if a quantifier is following. A quantifier without an atom
        // is an error.
        pos_backup = pos
        var quantifier = parseQuantifier() || false;
        if (quantifier) {
          pos = pos_backup
          bail('Expected atom');
        }

        // If no unicode flag, then try to parse ExtendedAtom -> ExtendedPatternCharacter.
        //      ExtendedPatternCharacter
        if (!hasUnicodeFlag && (res = matchReg(/^{/))) {
          atom = createCharacter(res);
        } else {
          bail('Expected atom');
        }
      }
      var quantifier = parseQuantifier() || false;
      if (quantifier) {
        quantifier.body = flattenBody(atom);
        // The quantifier contains the atom. Therefore, the beginning of the
        // quantifier range is given by the beginning of the atom.
        updateRawStart(quantifier, atom.range[0]);
        return quantifier;
      }
      return atom;
    }

    function parseGroup(matchA, typeA, matchB, typeB) {
      var type = null, from = pos;

      if (match(matchA)) {
        type = typeA;
      } else if (match(matchB)) {
        type = typeB;
      } else {
        return false;
      }

      return finishGroup(type, from);
    }

    function finishGroup(type, from) {
      var body = parseDisjunction();
      if (!body) {
        bail('Expected disjunction');
      }
      skip(')');
      var group = createGroup(type, flattenBody(body), from, pos);

      if (type == 'normal') {
        // Keep track of the number of closed groups. This is required for
        // parseDecimalEscape(). In case the string is parsed a second time the
        // value already holds the total count and no incrementation is required.
        if (firstIteration) {
          closedCaptureCounter++;
        }
      }
      return group;
    }

    function parseAnchor() {
      // Anchor ::
      //      ^
      //      $
      //      \ b
      //      \ B
      //      ( ? = Disjunction )
      //      ( ? ! Disjunction )
      var res, from = pos;

      if (match('^')) {
        return createAnchor('start', 1 /* rawLength */);
      } else if (match('$')) {
        return createAnchor('end', 1 /* rawLength */);
      } else if (match('\\b')) {
        return createAnchor('boundary', 2 /* rawLength */);
      } else if (match('\\B')) {
        return createAnchor('not-boundary', 2 /* rawLength */);
      } else {
        return parseGroup('(?=', 'lookahead', '(?!', 'negativeLookahead');
      }
    }

    function parseQuantifier() {
      // Quantifier ::
      //      QuantifierPrefix
      //      QuantifierPrefix ?
      //
      // QuantifierPrefix ::
      //      *
      //      +
      //      ?
      //      { DecimalDigits }
      //      { DecimalDigits , }
      //      { DecimalDigits , DecimalDigits }

      var res, from = pos;
      var quantifier;
      var min, max;

      if (match('*')) {
        quantifier = createQuantifier(0);
      }
      else if (match('+')) {
        quantifier = createQuantifier(1);
      }
      else if (match('?')) {
        quantifier = createQuantifier(0, 1);
      }
      else if (res = matchReg(/^\{([0-9]+)\}/)) {
        min = parseInt(res[1], 10);
        quantifier = createQuantifier(min, min, res.range[0], res.range[1]);
      }
      else if (res = matchReg(/^\{([0-9]+),\}/)) {
        min = parseInt(res[1], 10);
        quantifier = createQuantifier(min, undefined, res.range[0], res.range[1]);
      }
      else if (res = matchReg(/^\{([0-9]+),([0-9]+)\}/)) {
        min = parseInt(res[1], 10);
        max = parseInt(res[2], 10);
        if (min > max) {
          bail('numbers out of order in {} quantifier', '', from, pos);
        }
        quantifier = createQuantifier(min, max, res.range[0], res.range[1]);
      }

      if (quantifier) {
        if (match('?')) {
          quantifier.greedy = false;
          quantifier.range[1] += 1;
        }
      }

      return quantifier;
    }

    function parseAtomAndExtendedAtom() {
      // Parsing Atom and ExtendedAtom together due to redundancy.
      // ExtendedAtom is defined in Apendix B of the ECMA-262 standard.
      //
      // SEE: https://www.ecma-international.org/ecma-262/10.0/index.html#prod-annexB-ExtendedPatternCharacter
      //
      // Atom ::
      //      PatternCharacter
      //      .
      //      \ AtomEscape
      //      CharacterClass
      //      ( GroupSpecifier Disjunction )
      //      ( ? : Disjunction )
      // ExtendedAtom ::
      //      ExtendedPatternCharacter
      // ExtendedPatternCharacter ::
      //      SourceCharacter but not one of ^$\.*+?()[|

      var res;

      // jviereck: allow ']', '}' here as well to be compatible with browser's
      //   implementations: ']'.match(/]/);
      if (res = matchReg(/^[^^$\\.*+?()[\]{}|]/)) {
        //      PatternCharacter
        return createCharacter(res);
      }
      else if (!hasUnicodeFlag && (res = matchReg(/^(?:]|})/))) {
        //      ExtendedPatternCharacter, first part. See parseTerm.
        return createCharacter(res);
      }
      else if (match('.')) {
        //      .
        return createDot();
      }
      else if (match('\\')) {
        //      \ AtomEscape
        res = parseAtomEscape();
        if (!res) {
          if (!hasUnicodeFlag && lookahead() == 'c') {
            // B.1.4 ExtendedAtom
            // \[lookahead = c]
            return createValue('symbol', 92, pos - 1, pos);
          }
          bail('atomEscape');
        }
        return res;
      }
      else if (res = parseCharacterClass()) {
        return res;
      }
      else if (features.lookbehind && (res = parseGroup('(?<=', 'lookbehind', '(?<!', 'negativeLookbehind'))) {
        return res;
      }
      else if (features.namedGroups && match("(?<")) {
        var name = parseIdentifier();
        skip(">");
        var group = finishGroup("normal", name.range[0] - 3);
        group.name = name;
        return group;
      }
      else {
        //      ( Disjunction )
        //      ( ? : Disjunction )
        return parseGroup('(?:', 'ignore', '(', 'normal');
      }
    }

    function parseUnicodeSurrogatePairEscape(firstEscape) {
      if (hasUnicodeFlag) {
        var first, second;
        if (firstEscape.kind == 'unicodeEscape' &&
          (first = firstEscape.codePoint) >= 0xD800 && first <= 0xDBFF &&
          current('\\') && next('u') ) {
          var prevPos = pos;
          pos++;
          var secondEscape = parseClassEscape();
          if (secondEscape.kind == 'unicodeEscape' &&
            (second = secondEscape.codePoint) >= 0xDC00 && second <= 0xDFFF) {
            // Unicode surrogate pair
            firstEscape.range[1] = secondEscape.range[1];
            firstEscape.codePoint = (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
            firstEscape.type = 'value';
            firstEscape.kind = 'unicodeCodePointEscape';
            addRaw(firstEscape);
          }
          else {
            pos = prevPos;
          }
        }
      }
      return firstEscape;
    }

    function parseClassEscape() {
      return parseAtomEscape(true);
    }

    function parseAtomEscape(insideCharacterClass) {
      // AtomEscape ::
      //      DecimalEscape
      //      CharacterEscape
      //      CharacterClassEscape
      //      k GroupName

      var res, from = pos;

      res = parseDecimalEscape() || parseNamedReference();
      if (res) {
        return res;
      }

      // For ClassEscape
      if (insideCharacterClass) {
        //     b
        if (match('b')) {
          // 15.10.2.19
          // The production ClassEscape :: b evaluates by returning the
          // CharSet containing the one character <BS> (Unicode value 0008).
          return createEscaped('singleEscape', 0x0008, '\\b');
        } else if (match('B')) {
          bail('\\B not possible inside of CharacterClass', '', from);
        } else if (!hasUnicodeFlag && (res = matchReg(/^c([0-9])/))) {
          // B.1.4
          // c ClassControlLetter, ClassControlLetter = DecimalDigit
          return createEscaped('controlLetter', res[1] + 16, res[1], 2);
        } else if (!hasUnicodeFlag && (res = matchReg(/^c_/))) {
          // B.1.4
          // c ClassControlLetter, ClassControlLetter = _
          return createEscaped('controlLetter', 31, '_', 2);
        }
        //     [+U] -
        if (hasUnicodeFlag && match('-')) {
          return createEscaped('singleEscape', 0x002d, '\\-');
        }
      }

      res = parseCharacterClassEscape() || parseCharacterEscape();

      return res;
    }


    function parseDecimalEscape() {
      // DecimalEscape ::
      //      DecimalIntegerLiteral [lookahead ∉ DecimalDigit]

      var res, match;

      if (res = matchReg(/^(?!0)\d+/)) {
        match = res[0];
        var refIdx = parseInt(res[0], 10);
        if (refIdx <= closedCaptureCounter) {
          // If the number is smaller than the normal-groups found so
          // far, then it is a reference...
          return createReference(res[0]);
        } else {
          // ... otherwise it needs to be interpreted as a octal (if the
          // number is in an octal format). If it is NOT octal format,
          // then the slash is ignored and the number is matched later
          // as normal characters.

          // Recall the negative decision to decide if the input must be parsed
          // a second time with the total normal-groups.
          backrefDenied.push(refIdx);

          // Reset the position again, as maybe only parts of the previous
          // matched numbers are actual octal numbers. E.g. in '019' only
          // the '01' should be matched.
          incr(-res[0].length);
          if (res = matchReg(/^[0-7]{1,3}/)) {
            return createEscaped('octal', parseInt(res[0], 8), res[0], 1);
          } else {
            // If we end up here, we have a case like /\91/. Then the
            // first slash is to be ignored and the 9 & 1 to be treated
            // like ordinary characters. Create a character for the
            // first number only here - other number-characters
            // (if available) will be matched later.
            res = createCharacter(matchReg(/^[89]/));
            return updateRawStart(res, res.range[0] - 1);
          }
        }
      }
      // Only allow octal numbers in the following. All matched numbers start
      // with a zero (if the do not, the previous if-branch is executed).
      // If the number is not octal format and starts with zero (e.g. `091`)
      // then only the zeros `0` is treated here and the `91` are ordinary
      // characters.
      // Example:
      //   /\091/.exec('\091')[0].length === 3
      else if (res = matchReg(/^[0-7]{1,3}/)) {
        match = res[0];
        if (/^0{1,3}$/.test(match)) {
          // If they are all zeros, then only take the first one.
          return createEscaped('null', 0x0000, '0', match.length);
        } else {
          return createEscaped('octal', parseInt(match, 8), match, 1);
        }
      }
      return false;
    }

    function parseCharacterClassEscape() {
      // CharacterClassEscape :: one of d D s S w W
      var res;
      if (res = matchReg(/^[dDsSwW]/)) {
        return createCharacterClassEscape(res[0]);
      } else if (features.unicodePropertyEscape && (hasUnicodeFlag || hasUnicodeSetFlag) && (res = matchReg(/^([pP])\{([^\}]+)\}/))) {
        // https://github.com/jviereck/regjsparser/issues/77
        return addRaw({
          type: 'unicodePropertyEscape',
          negative: res[1] === 'P',
          value: res[2],
          range: [res.range[0] - 1, res.range[1]],
          raw: res[0]
        });
      }
      return false;
    }

    function parseNamedReference() {
      if (features.namedGroups && matchReg(/^k<(?=.*?>)/)) {
        var name = parseIdentifier();
        skip('>');
        return createNamedReference(name);
      }
    }

    function parseRegExpUnicodeEscapeSequence() {
      var res;
      if (res = matchReg(/^u([0-9a-fA-F]{4})/)) {
        // UnicodeEscapeSequence
        return parseUnicodeSurrogatePairEscape(
          createEscaped('unicodeEscape', parseInt(res[1], 16), res[1], 2)
        );
      } else if (hasUnicodeFlag && (res = matchReg(/^u\{([0-9a-fA-F]+)\}/))) {
        // RegExpUnicodeEscapeSequence (ES6 Unicode code point escape)
        return createEscaped('unicodeCodePointEscape', parseInt(res[1], 16), res[1], 4);
      }
    }

    function parseCharacterEscape() {
      // CharacterEscape ::
      //      ControlEscape
      //      c ControlLetter
      //      HexEscapeSequence
      //      UnicodeEscapeSequence
      //      IdentityEscape

      var res;
      var from = pos;
      if (res = matchReg(/^[fnrtv]/)) {
        // ControlEscape
        var codePoint = 0;
        switch (res[0]) {
          case 't': codePoint = 0x009; break;
          case 'n': codePoint = 0x00A; break;
          case 'v': codePoint = 0x00B; break;
          case 'f': codePoint = 0x00C; break;
          case 'r': codePoint = 0x00D; break;
        }
        return createEscaped('singleEscape', codePoint, '\\' + res[0]);
      } else if (res = matchReg(/^c([a-zA-Z])/)) {
        // c ControlLetter
        return createEscaped('controlLetter', res[1].charCodeAt(0) % 32, res[1], 2);
      } else if (res = matchReg(/^x([0-9a-fA-F]{2})/)) {
        // HexEscapeSequence
        return createEscaped('hexadecimalEscape', parseInt(res[1], 16), res[1], 2);
      } else if (res = parseRegExpUnicodeEscapeSequence()) {
        if (!res || res.codePoint > 0x10FFFF) {
          bail('Invalid escape sequence', null, from, pos);
        }
        return res;
      } else {
        // IdentityEscape
        return parseIdentityEscape();
      }
    }

    function parseIdentifierAtom(check) {
      var ch = lookahead();
      var from = pos;
      if (ch === '\\') {
        incr();
        var esc = parseRegExpUnicodeEscapeSequence();
        if (!esc || !check(esc.codePoint)) {
          bail('Invalid escape sequence', null, from, pos);
        }
        return fromCodePoint(esc.codePoint);
      }
      var code = ch.charCodeAt(0);
      if (code >= 0xD800 && code <= 0xDBFF) {
        ch += str[pos + 1];
        var second = ch.charCodeAt(1);
        if (second >= 0xDC00 && second <= 0xDFFF) {
          // Unicode surrogate pair
          code = (code - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
        }
      }
      if (!check(code)) return;
      incr();
      if (code > 0xFFFF) incr();
      return ch;
    }

    function parseIdentifier() {
      // RegExpIdentifierName ::
      //      RegExpIdentifierStart
      //      RegExpIdentifierName RegExpIdentifierContinue
      //
      // RegExpIdentifierStart ::
      //      UnicodeIDStart
      //      $
      //      _
      //      \ RegExpUnicodeEscapeSequence
      //
      // RegExpIdentifierContinue ::
      //      UnicodeIDContinue
      //      $
      //      _
      //      \ RegExpUnicodeEscapeSequence
      //      <ZWNJ>
      //      <ZWJ>

      var start = pos;
      var res = parseIdentifierAtom(isIdentifierStart);
      if (!res) {
        bail('Invalid identifier');
      }

      var ch;
      while (ch = parseIdentifierAtom(isIdentifierPart)) {
        res += ch;
      }

      return addRaw({
        type: 'identifier',
        value: res,
        range: [start, pos]
      });
    }

    function isIdentifierStart(ch) {
      // Generated by `tools/generate-identifier-regex.js`.
      var NonAsciiIdentifierStart = /[\$A-Z_a-z\xAA\xB5\xBA\xC0-\xD6\xD8-\xF6\xF8-\u02C1\u02C6-\u02D1\u02E0-\u02E4\u02EC\u02EE\u0370-\u0374\u0376\u0377\u037A-\u037D\u037F\u0386\u0388-\u038A\u038C\u038E-\u03A1\u03A3-\u03F5\u03F7-\u0481\u048A-\u052F\u0531-\u0556\u0559\u0560-\u0588\u05D0-\u05EA\u05EF-\u05F2\u0620-\u064A\u066E\u066F\u0671-\u06D3\u06D5\u06E5\u06E6\u06EE\u06EF\u06FA-\u06FC\u06FF\u0710\u0712-\u072F\u074D-\u07A5\u07B1\u07CA-\u07EA\u07F4\u07F5\u07FA\u0800-\u0815\u081A\u0824\u0828\u0840-\u0858\u0860-\u086A\u08A0-\u08B4\u08B6-\u08BD\u0904-\u0939\u093D\u0950\u0958-\u0961\u0971-\u0980\u0985-\u098C\u098F\u0990\u0993-\u09A8\u09AA-\u09B0\u09B2\u09B6-\u09B9\u09BD\u09CE\u09DC\u09DD\u09DF-\u09E1\u09F0\u09F1\u09FC\u0A05-\u0A0A\u0A0F\u0A10\u0A13-\u0A28\u0A2A-\u0A30\u0A32\u0A33\u0A35\u0A36\u0A38\u0A39\u0A59-\u0A5C\u0A5E\u0A72-\u0A74\u0A85-\u0A8D\u0A8F-\u0A91\u0A93-\u0AA8\u0AAA-\u0AB0\u0AB2\u0AB3\u0AB5-\u0AB9\u0ABD\u0AD0\u0AE0\u0AE1\u0AF9\u0B05-\u0B0C\u0B0F\u0B10\u0B13-\u0B28\u0B2A-\u0B30\u0B32\u0B33\u0B35-\u0B39\u0B3D\u0B5C\u0B5D\u0B5F-\u0B61\u0B71\u0B83\u0B85-\u0B8A\u0B8E-\u0B90\u0B92-\u0B95\u0B99\u0B9A\u0B9C\u0B9E\u0B9F\u0BA3\u0BA4\u0BA8-\u0BAA\u0BAE-\u0BB9\u0BD0\u0C05-\u0C0C\u0C0E-\u0C10\u0C12-\u0C28\u0C2A-\u0C39\u0C3D\u0C58-\u0C5A\u0C60\u0C61\u0C80\u0C85-\u0C8C\u0C8E-\u0C90\u0C92-\u0CA8\u0CAA-\u0CB3\u0CB5-\u0CB9\u0CBD\u0CDE\u0CE0\u0CE1\u0CF1\u0CF2\u0D05-\u0D0C\u0D0E-\u0D10\u0D12-\u0D3A\u0D3D\u0D4E\u0D54-\u0D56\u0D5F-\u0D61\u0D7A-\u0D7F\u0D85-\u0D96\u0D9A-\u0DB1\u0DB3-\u0DBB\u0DBD\u0DC0-\u0DC6\u0E01-\u0E30\u0E32\u0E33\u0E40-\u0E46\u0E81\u0E82\u0E84\u0E87\u0E88\u0E8A\u0E8D\u0E94-\u0E97\u0E99-\u0E9F\u0EA1-\u0EA3\u0EA5\u0EA7\u0EAA\u0EAB\u0EAD-\u0EB0\u0EB2\u0EB3\u0EBD\u0EC0-\u0EC4\u0EC6\u0EDC-\u0EDF\u0F00\u0F40-\u0F47\u0F49-\u0F6C\u0F88-\u0F8C\u1000-\u102A\u103F\u1050-\u1055\u105A-\u105D\u1061\u1065\u1066\u106E-\u1070\u1075-\u1081\u108E\u10A0-\u10C5\u10C7\u10CD\u10D0-\u10FA\u10FC-\u1248\u124A-\u124D\u1250-\u1256\u1258\u125A-\u125D\u1260-\u1288\u128A-\u128D\u1290-\u12B0\u12B2-\u12B5\u12B8-\u12BE\u12C0\u12C2-\u12C5\u12C8-\u12D6\u12D8-\u1310\u1312-\u1315\u1318-\u135A\u1380-\u138F\u13A0-\u13F5\u13F8-\u13FD\u1401-\u166C\u166F-\u167F\u1681-\u169A\u16A0-\u16EA\u16EE-\u16F8\u1700-\u170C\u170E-\u1711\u1720-\u1731\u1740-\u1751\u1760-\u176C\u176E-\u1770\u1780-\u17B3\u17D7\u17DC\u1820-\u1878\u1880-\u18A8\u18AA\u18B0-\u18F5\u1900-\u191E\u1950-\u196D\u1970-\u1974\u1980-\u19AB\u19B0-\u19C9\u1A00-\u1A16\u1A20-\u1A54\u1AA7\u1B05-\u1B33\u1B45-\u1B4B\u1B83-\u1BA0\u1BAE\u1BAF\u1BBA-\u1BE5\u1C00-\u1C23\u1C4D-\u1C4F\u1C5A-\u1C7D\u1C80-\u1C88\u1C90-\u1CBA\u1CBD-\u1CBF\u1CE9-\u1CEC\u1CEE-\u1CF1\u1CF5\u1CF6\u1D00-\u1DBF\u1E00-\u1F15\u1F18-\u1F1D\u1F20-\u1F45\u1F48-\u1F4D\u1F50-\u1F57\u1F59\u1F5B\u1F5D\u1F5F-\u1F7D\u1F80-\u1FB4\u1FB6-\u1FBC\u1FBE\u1FC2-\u1FC4\u1FC6-\u1FCC\u1FD0-\u1FD3\u1FD6-\u1FDB\u1FE0-\u1FEC\u1FF2-\u1FF4\u1FF6-\u1FFC\u2071\u207F\u2090-\u209C\u2102\u2107\u210A-\u2113\u2115\u2118-\u211D\u2124\u2126\u2128\u212A-\u2139\u213C-\u213F\u2145-\u2149\u214E\u2160-\u2188\u2C00-\u2C2E\u2C30-\u2C5E\u2C60-\u2CE4\u2CEB-\u2CEE\u2CF2\u2CF3\u2D00-\u2D25\u2D27\u2D2D\u2D30-\u2D67\u2D6F\u2D80-\u2D96\u2DA0-\u2DA6\u2DA8-\u2DAE\u2DB0-\u2DB6\u2DB8-\u2DBE\u2DC0-\u2DC6\u2DC8-\u2DCE\u2DD0-\u2DD6\u2DD8-\u2DDE\u3005-\u3007\u3021-\u3029\u3031-\u3035\u3038-\u303C\u3041-\u3096\u309B-\u309F\u30A1-\u30FA\u30FC-\u30FF\u3105-\u312F\u3131-\u318E\u31A0-\u31BA\u31F0-\u31FF\u3400-\u4DB5\u4E00-\u9FEF\uA000-\uA48C\uA4D0-\uA4FD\uA500-\uA60C\uA610-\uA61F\uA62A\uA62B\uA640-\uA66E\uA67F-\uA69D\uA6A0-\uA6EF\uA717-\uA71F\uA722-\uA788\uA78B-\uA7B9\uA7F7-\uA801\uA803-\uA805\uA807-\uA80A\uA80C-\uA822\uA840-\uA873\uA882-\uA8B3\uA8F2-\uA8F7\uA8FB\uA8FD\uA8FE\uA90A-\uA925\uA930-\uA946\uA960-\uA97C\uA984-\uA9B2\uA9CF\uA9E0-\uA9E4\uA9E6-\uA9EF\uA9FA-\uA9FE\uAA00-\uAA28\uAA40-\uAA42\uAA44-\uAA4B\uAA60-\uAA76\uAA7A\uAA7E-\uAAAF\uAAB1\uAAB5\uAAB6\uAAB9-\uAABD\uAAC0\uAAC2\uAADB-\uAADD\uAAE0-\uAAEA\uAAF2-\uAAF4\uAB01-\uAB06\uAB09-\uAB0E\uAB11-\uAB16\uAB20-\uAB26\uAB28-\uAB2E\uAB30-\uAB5A\uAB5C-\uAB65\uAB70-\uABE2\uAC00-\uD7A3\uD7B0-\uD7C6\uD7CB-\uD7FB\uF900-\uFA6D\uFA70-\uFAD9\uFB00-\uFB06\uFB13-\uFB17\uFB1D\uFB1F-\uFB28\uFB2A-\uFB36\uFB38-\uFB3C\uFB3E\uFB40\uFB41\uFB43\uFB44\uFB46-\uFBB1\uFBD3-\uFD3D\uFD50-\uFD8F\uFD92-\uFDC7\uFDF0-\uFDFB\uFE70-\uFE74\uFE76-\uFEFC\uFF21-\uFF3A\uFF41-\uFF5A\uFF66-\uFFBE\uFFC2-\uFFC7\uFFCA-\uFFCF\uFFD2-\uFFD7\uFFDA-\uFFDC]|\uD800[\uDC00-\uDC0B\uDC0D-\uDC26\uDC28-\uDC3A\uDC3C\uDC3D\uDC3F-\uDC4D\uDC50-\uDC5D\uDC80-\uDCFA\uDD40-\uDD74\uDE80-\uDE9C\uDEA0-\uDED0\uDF00-\uDF1F\uDF2D-\uDF4A\uDF50-\uDF75\uDF80-\uDF9D\uDFA0-\uDFC3\uDFC8-\uDFCF\uDFD1-\uDFD5]|\uD801[\uDC00-\uDC9D\uDCB0-\uDCD3\uDCD8-\uDCFB\uDD00-\uDD27\uDD30-\uDD63\uDE00-\uDF36\uDF40-\uDF55\uDF60-\uDF67]|\uD802[\uDC00-\uDC05\uDC08\uDC0A-\uDC35\uDC37\uDC38\uDC3C\uDC3F-\uDC55\uDC60-\uDC76\uDC80-\uDC9E\uDCE0-\uDCF2\uDCF4\uDCF5\uDD00-\uDD15\uDD20-\uDD39\uDD80-\uDDB7\uDDBE\uDDBF\uDE00\uDE10-\uDE13\uDE15-\uDE17\uDE19-\uDE35\uDE60-\uDE7C\uDE80-\uDE9C\uDEC0-\uDEC7\uDEC9-\uDEE4\uDF00-\uDF35\uDF40-\uDF55\uDF60-\uDF72\uDF80-\uDF91]|\uD803[\uDC00-\uDC48\uDC80-\uDCB2\uDCC0-\uDCF2\uDD00-\uDD23\uDF00-\uDF1C\uDF27\uDF30-\uDF45]|\uD804[\uDC03-\uDC37\uDC83-\uDCAF\uDCD0-\uDCE8\uDD03-\uDD26\uDD44\uDD50-\uDD72\uDD76\uDD83-\uDDB2\uDDC1-\uDDC4\uDDDA\uDDDC\uDE00-\uDE11\uDE13-\uDE2B\uDE80-\uDE86\uDE88\uDE8A-\uDE8D\uDE8F-\uDE9D\uDE9F-\uDEA8\uDEB0-\uDEDE\uDF05-\uDF0C\uDF0F\uDF10\uDF13-\uDF28\uDF2A-\uDF30\uDF32\uDF33\uDF35-\uDF39\uDF3D\uDF50\uDF5D-\uDF61]|\uD805[\uDC00-\uDC34\uDC47-\uDC4A\uDC80-\uDCAF\uDCC4\uDCC5\uDCC7\uDD80-\uDDAE\uDDD8-\uDDDB\uDE00-\uDE2F\uDE44\uDE80-\uDEAA\uDF00-\uDF1A]|\uD806[\uDC00-\uDC2B\uDCA0-\uDCDF\uDCFF\uDE00\uDE0B-\uDE32\uDE3A\uDE50\uDE5C-\uDE83\uDE86-\uDE89\uDE9D\uDEC0-\uDEF8]|\uD807[\uDC00-\uDC08\uDC0A-\uDC2E\uDC40\uDC72-\uDC8F\uDD00-\uDD06\uDD08\uDD09\uDD0B-\uDD30\uDD46\uDD60-\uDD65\uDD67\uDD68\uDD6A-\uDD89\uDD98\uDEE0-\uDEF2]|\uD808[\uDC00-\uDF99]|\uD809[\uDC00-\uDC6E\uDC80-\uDD43]|[\uD80C\uD81C-\uD820\uD840-\uD868\uD86A-\uD86C\uD86F-\uD872\uD874-\uD879][\uDC00-\uDFFF]|\uD80D[\uDC00-\uDC2E]|\uD811[\uDC00-\uDE46]|\uD81A[\uDC00-\uDE38\uDE40-\uDE5E\uDED0-\uDEED\uDF00-\uDF2F\uDF40-\uDF43\uDF63-\uDF77\uDF7D-\uDF8F]|\uD81B[\uDE40-\uDE7F\uDF00-\uDF44\uDF50\uDF93-\uDF9F\uDFE0\uDFE1]|\uD821[\uDC00-\uDFF1]|\uD822[\uDC00-\uDEF2]|\uD82C[\uDC00-\uDD1E\uDD70-\uDEFB]|\uD82F[\uDC00-\uDC6A\uDC70-\uDC7C\uDC80-\uDC88\uDC90-\uDC99]|\uD835[\uDC00-\uDC54\uDC56-\uDC9C\uDC9E\uDC9F\uDCA2\uDCA5\uDCA6\uDCA9-\uDCAC\uDCAE-\uDCB9\uDCBB\uDCBD-\uDCC3\uDCC5-\uDD05\uDD07-\uDD0A\uDD0D-\uDD14\uDD16-\uDD1C\uDD1E-\uDD39\uDD3B-\uDD3E\uDD40-\uDD44\uDD46\uDD4A-\uDD50\uDD52-\uDEA5\uDEA8-\uDEC0\uDEC2-\uDEDA\uDEDC-\uDEFA\uDEFC-\uDF14\uDF16-\uDF34\uDF36-\uDF4E\uDF50-\uDF6E\uDF70-\uDF88\uDF8A-\uDFA8\uDFAA-\uDFC2\uDFC4-\uDFCB]|\uD83A[\uDC00-\uDCC4\uDD00-\uDD43]|\uD83B[\uDE00-\uDE03\uDE05-\uDE1F\uDE21\uDE22\uDE24\uDE27\uDE29-\uDE32\uDE34-\uDE37\uDE39\uDE3B\uDE42\uDE47\uDE49\uDE4B\uDE4D-\uDE4F\uDE51\uDE52\uDE54\uDE57\uDE59\uDE5B\uDE5D\uDE5F\uDE61\uDE62\uDE64\uDE67-\uDE6A\uDE6C-\uDE72\uDE74-\uDE77\uDE79-\uDE7C\uDE7E\uDE80-\uDE89\uDE8B-\uDE9B\uDEA1-\uDEA3\uDEA5-\uDEA9\uDEAB-\uDEBB]|\uD869[\uDC00-\uDED6\uDF00-\uDFFF]|\uD86D[\uDC00-\uDF34\uDF40-\uDFFF]|\uD86E[\uDC00-\uDC1D\uDC20-\uDFFF]|\uD873[\uDC00-\uDEA1\uDEB0-\uDFFF]|\uD87A[\uDC00-\uDFE0]|\uD87E[\uDC00-\uDE1D]/;

      return (ch === 36) || (ch === 95) ||  // $ (dollar) and _ (underscore)
        (ch >= 65 && ch <= 90) ||         // A..Z
        (ch >= 97 && ch <= 122) ||        // a..z
        ((ch >= 0x80) && NonAsciiIdentifierStart.test(fromCodePoint(ch)));
    }

    // Taken from the Esprima parser.
    function isIdentifierPart(ch) {
      // Generated by `tools/generate-identifier-regex.js`.
      var NonAsciiIdentifierPartOnly = /[0-9_\xB7\u0300-\u036F\u0387\u0483-\u0487\u0591-\u05BD\u05BF\u05C1\u05C2\u05C4\u05C5\u05C7\u0610-\u061A\u064B-\u0669\u0670\u06D6-\u06DC\u06DF-\u06E4\u06E7\u06E8\u06EA-\u06ED\u06F0-\u06F9\u0711\u0730-\u074A\u07A6-\u07B0\u07C0-\u07C9\u07EB-\u07F3\u07FD\u0816-\u0819\u081B-\u0823\u0825-\u0827\u0829-\u082D\u0859-\u085B\u08D3-\u08E1\u08E3-\u0903\u093A-\u093C\u093E-\u094F\u0951-\u0957\u0962\u0963\u0966-\u096F\u0981-\u0983\u09BC\u09BE-\u09C4\u09C7\u09C8\u09CB-\u09CD\u09D7\u09E2\u09E3\u09E6-\u09EF\u09FE\u0A01-\u0A03\u0A3C\u0A3E-\u0A42\u0A47\u0A48\u0A4B-\u0A4D\u0A51\u0A66-\u0A71\u0A75\u0A81-\u0A83\u0ABC\u0ABE-\u0AC5\u0AC7-\u0AC9\u0ACB-\u0ACD\u0AE2\u0AE3\u0AE6-\u0AEF\u0AFA-\u0AFF\u0B01-\u0B03\u0B3C\u0B3E-\u0B44\u0B47\u0B48\u0B4B-\u0B4D\u0B56\u0B57\u0B62\u0B63\u0B66-\u0B6F\u0B82\u0BBE-\u0BC2\u0BC6-\u0BC8\u0BCA-\u0BCD\u0BD7\u0BE6-\u0BEF\u0C00-\u0C04\u0C3E-\u0C44\u0C46-\u0C48\u0C4A-\u0C4D\u0C55\u0C56\u0C62\u0C63\u0C66-\u0C6F\u0C81-\u0C83\u0CBC\u0CBE-\u0CC4\u0CC6-\u0CC8\u0CCA-\u0CCD\u0CD5\u0CD6\u0CE2\u0CE3\u0CE6-\u0CEF\u0D00-\u0D03\u0D3B\u0D3C\u0D3E-\u0D44\u0D46-\u0D48\u0D4A-\u0D4D\u0D57\u0D62\u0D63\u0D66-\u0D6F\u0D82\u0D83\u0DCA\u0DCF-\u0DD4\u0DD6\u0DD8-\u0DDF\u0DE6-\u0DEF\u0DF2\u0DF3\u0E31\u0E34-\u0E3A\u0E47-\u0E4E\u0E50-\u0E59\u0EB1\u0EB4-\u0EB9\u0EBB\u0EBC\u0EC8-\u0ECD\u0ED0-\u0ED9\u0F18\u0F19\u0F20-\u0F29\u0F35\u0F37\u0F39\u0F3E\u0F3F\u0F71-\u0F84\u0F86\u0F87\u0F8D-\u0F97\u0F99-\u0FBC\u0FC6\u102B-\u103E\u1040-\u1049\u1056-\u1059\u105E-\u1060\u1062-\u1064\u1067-\u106D\u1071-\u1074\u1082-\u108D\u108F-\u109D\u135D-\u135F\u1369-\u1371\u1712-\u1714\u1732-\u1734\u1752\u1753\u1772\u1773\u17B4-\u17D3\u17DD\u17E0-\u17E9\u180B-\u180D\u1810-\u1819\u18A9\u1920-\u192B\u1930-\u193B\u1946-\u194F\u19D0-\u19DA\u1A17-\u1A1B\u1A55-\u1A5E\u1A60-\u1A7C\u1A7F-\u1A89\u1A90-\u1A99\u1AB0-\u1ABD\u1B00-\u1B04\u1B34-\u1B44\u1B50-\u1B59\u1B6B-\u1B73\u1B80-\u1B82\u1BA1-\u1BAD\u1BB0-\u1BB9\u1BE6-\u1BF3\u1C24-\u1C37\u1C40-\u1C49\u1C50-\u1C59\u1CD0-\u1CD2\u1CD4-\u1CE8\u1CED\u1CF2-\u1CF4\u1CF7-\u1CF9\u1DC0-\u1DF9\u1DFB-\u1DFF\u200C\u200D\u203F\u2040\u2054\u20D0-\u20DC\u20E1\u20E5-\u20F0\u2CEF-\u2CF1\u2D7F\u2DE0-\u2DFF\u302A-\u302F\u3099\u309A\uA620-\uA629\uA66F\uA674-\uA67D\uA69E\uA69F\uA6F0\uA6F1\uA802\uA806\uA80B\uA823-\uA827\uA880\uA881\uA8B4-\uA8C5\uA8D0-\uA8D9\uA8E0-\uA8F1\uA8FF-\uA909\uA926-\uA92D\uA947-\uA953\uA980-\uA983\uA9B3-\uA9C0\uA9D0-\uA9D9\uA9E5\uA9F0-\uA9F9\uAA29-\uAA36\uAA43\uAA4C\uAA4D\uAA50-\uAA59\uAA7B-\uAA7D\uAAB0\uAAB2-\uAAB4\uAAB7\uAAB8\uAABE\uAABF\uAAC1\uAAEB-\uAAEF\uAAF5\uAAF6\uABE3-\uABEA\uABEC\uABED\uABF0-\uABF9\uFB1E\uFE00-\uFE0F\uFE20-\uFE2F\uFE33\uFE34\uFE4D-\uFE4F\uFF10-\uFF19\uFF3F]|\uD800[\uDDFD\uDEE0\uDF76-\uDF7A]|\uD801[\uDCA0-\uDCA9]|\uD802[\uDE01-\uDE03\uDE05\uDE06\uDE0C-\uDE0F\uDE38-\uDE3A\uDE3F\uDEE5\uDEE6]|\uD803[\uDD24-\uDD27\uDD30-\uDD39\uDF46-\uDF50]|\uD804[\uDC00-\uDC02\uDC38-\uDC46\uDC66-\uDC6F\uDC7F-\uDC82\uDCB0-\uDCBA\uDCF0-\uDCF9\uDD00-\uDD02\uDD27-\uDD34\uDD36-\uDD3F\uDD45\uDD46\uDD73\uDD80-\uDD82\uDDB3-\uDDC0\uDDC9-\uDDCC\uDDD0-\uDDD9\uDE2C-\uDE37\uDE3E\uDEDF-\uDEEA\uDEF0-\uDEF9\uDF00-\uDF03\uDF3B\uDF3C\uDF3E-\uDF44\uDF47\uDF48\uDF4B-\uDF4D\uDF57\uDF62\uDF63\uDF66-\uDF6C\uDF70-\uDF74]|\uD805[\uDC35-\uDC46\uDC50-\uDC59\uDC5E\uDCB0-\uDCC3\uDCD0-\uDCD9\uDDAF-\uDDB5\uDDB8-\uDDC0\uDDDC\uDDDD\uDE30-\uDE40\uDE50-\uDE59\uDEAB-\uDEB7\uDEC0-\uDEC9\uDF1D-\uDF2B\uDF30-\uDF39]|\uD806[\uDC2C-\uDC3A\uDCE0-\uDCE9\uDE01-\uDE0A\uDE33-\uDE39\uDE3B-\uDE3E\uDE47\uDE51-\uDE5B\uDE8A-\uDE99]|\uD807[\uDC2F-\uDC36\uDC38-\uDC3F\uDC50-\uDC59\uDC92-\uDCA7\uDCA9-\uDCB6\uDD31-\uDD36\uDD3A\uDD3C\uDD3D\uDD3F-\uDD45\uDD47\uDD50-\uDD59\uDD8A-\uDD8E\uDD90\uDD91\uDD93-\uDD97\uDDA0-\uDDA9\uDEF3-\uDEF6]|\uD81A[\uDE60-\uDE69\uDEF0-\uDEF4\uDF30-\uDF36\uDF50-\uDF59]|\uD81B[\uDF51-\uDF7E\uDF8F-\uDF92]|\uD82F[\uDC9D\uDC9E]|\uD834[\uDD65-\uDD69\uDD6D-\uDD72\uDD7B-\uDD82\uDD85-\uDD8B\uDDAA-\uDDAD\uDE42-\uDE44]|\uD835[\uDFCE-\uDFFF]|\uD836[\uDE00-\uDE36\uDE3B-\uDE6C\uDE75\uDE84\uDE9B-\uDE9F\uDEA1-\uDEAF]|\uD838[\uDC00-\uDC06\uDC08-\uDC18\uDC1B-\uDC21\uDC23\uDC24\uDC26-\uDC2A]|\uD83A[\uDCD0-\uDCD6\uDD44-\uDD4A\uDD50-\uDD59]|\uDB40[\uDD00-\uDDEF]/;

      return isIdentifierStart(ch) ||
        (ch >= 48 && ch <= 57) ||         // 0..9
        ((ch >= 0x80) && NonAsciiIdentifierPartOnly.test(fromCodePoint(ch)));
    }

    function parseIdentityEscape() {
      // IdentityEscape ::
      //      [+U] SyntaxCharacter
      //      [+U] /
      //      [~U] SourceCharacterIdentityEscape[?N]
      // SourceCharacterIdentityEscape[?N] ::
      //      [~N] SourceCharacter but not c
      //      [+N] SourceCharacter but not one of c or k


      var tmp;
      var l = lookahead();
      if (
        (hasUnicodeFlag && /[\^\$\.\*\+\?\(\)\\\[\]\{\}\|\/]/.test(l)) ||
        (!hasUnicodeFlag && l !== "c")
      ) {
        if (l === "k" && features.lookbehind) {
          return null;
        }
        tmp = incr();
        return createEscaped('identifier', tmp.charCodeAt(0), tmp, 1);
      }

      return null;
    }

    function parseCharacterClass() {
      // CharacterClass ::
      //      [ [lookahead ∉ {^}] ClassRanges ]
      //      [ ^ ClassRanges ]

      var res, from = pos;
      if (res = matchReg(/^\[\^/)) {
        res = parseClassRanges();
        skip(']');
        return createCharacterClass(res, true, from, pos);
      } else if (match('[')) {
        res = parseClassRanges();
        skip(']');
        return createCharacterClass(res, false, from, pos);
      }

      return null;
    }

    function parseClassRanges() {
      // ClassRanges ::
      //      [empty]
      //      [~V] NonemptyClassRanges
      //      [+V] ClassContents

      var res;
      if (current(']')) {
        // Empty array means nothing inside of the ClassRange.
        return { kind: 'union', body: [] };
      } else if (hasUnicodeSetFlag) {
        return parseClassContents();
      } else {
        res = parseNonemptyClassRanges();
        if (!res) {
          bail('nonEmptyClassRanges');
        }
        return { kind: 'union', body: res };
      }
    }

    function parseHelperClassRanges(atom) {
      var from, to, res, atomTo, dash;
      if (current('-') && !next(']')) {
        // ClassAtom - ClassAtom ClassRanges
        from = atom.range[0];
        dash = createCharacter(match('-'));

        atomTo = parseClassAtom();
        if (!atomTo) {
          bail('classAtom');
        }
        to = pos;

        // Parse the next class range if exists.
        var classRanges = parseClassRanges();
        if (!classRanges) {
          bail('classRanges');
        }

        // Check if both the from and atomTo have codePoints.
        if (!('codePoint' in atom) || !('codePoint' in atomTo)) {
            if (!hasUnicodeFlag) {
                // If not, don't create a range but treat them as
                // `atom` `-` `atom` instead.
                //
                // SEE: https://tc39.es/ecma262/#sec-regular-expression-patterns-semantics
                //   NonemptyClassRanges::ClassAtom-ClassAtomClassRanges
                //   CharacterRangeOrUnion
                res = [atom, dash, atomTo];
            } else {
                // With unicode flag, both sides must have codePoints if
                // one side has a codePoint.
                //
                // SEE: https://tc39.es/ecma262/#sec-patterns-static-semantics-early-errors
                //   NonemptyClassRanges :: ClassAtom - ClassAtom ClassRanges
                bail('invalid character class');
            }
        } else {
            res = [createClassRange(atom, atomTo, from, to)];
        }

        if (classRanges.type === 'empty') {
          return res;
        }
        return res.concat(classRanges.body);
      }

      res = parseNonemptyClassRangesNoDash();
      if (!res) {
        bail('nonEmptyClassRangesNoDash');
      }

      return [atom].concat(res);
    }

    function parseNonemptyClassRanges() {
      // NonemptyClassRanges ::
      //      ClassAtom
      //      ClassAtom NonemptyClassRangesNoDash
      //      ClassAtom - ClassAtom ClassRanges

      var atom = parseClassAtom();
      if (!atom) {
        bail('classAtom');
      }

      if (current(']')) {
        // ClassAtom
        return [atom];
      }

      // ClassAtom NonemptyClassRangesNoDash
      // ClassAtom - ClassAtom ClassRanges
      return parseHelperClassRanges(atom);
    }

    function parseNonemptyClassRangesNoDash() {
      // NonemptyClassRangesNoDash ::
      //      ClassAtom
      //      ClassAtomNoDash NonemptyClassRangesNoDash
      //      ClassAtomNoDash - ClassAtom ClassRanges

      var res = parseClassAtom();
      if (!res) {
        bail('classAtom');
      }
      if (current(']')) {
        //      ClassAtom
        return res;
      }

      // ClassAtomNoDash NonemptyClassRangesNoDash
      // ClassAtomNoDash - ClassAtom ClassRanges
      return parseHelperClassRanges(res);
    }

    function parseClassAtom() {
      // ClassAtom ::
      //      -
      //      ClassAtomNoDash
      if (match('-')) {
        return createCharacter('-');
      } else {
        return parseClassAtomNoDash();
      }
    }

    function parseClassAtomNoDash() {
      // ClassAtomNoDash ::
      //      SourceCharacter but not one of \ or ] or -
      //      \ ClassEscape

      var res;
      if (res = matchReg(/^[^\\\]-]/)) {
        return createCharacter(res[0]);
      } else if (match('\\')) {
        res = parseClassEscape();
        if (!res) {
          bail('classEscape');
        }

        return parseUnicodeSurrogatePairEscape(res);
      }
    }

    function parseClassContents() {
      // ClassContents ::
      //      ClassUnion
      //      ClassIntersection
      //      ClassSubtraction
      //
      // ClassUnion ::
      //      ClassRange ClassUnion?
      //      ClassOperand ClassUnion?
      //
      // ClassIntersection ::
      //      ClassOperand && [lookahead ≠ &] ClassOperand
      //      ClassIntersection && [lookahead ≠ &] ClassOperand
      //
      // ClassSubtraction ::
      //      ClassOperand -- ClassOperand
      //      ClassSubtraction -- ClassOperand

      var body = [];
      var kind;
      var from = pos;

      var operand = parseClassOperand(/* allowRanges*/ true);
      body.push(operand);

      if (operand.type === 'classRange') {
        kind = 'union';
      } else if (current('&')) {
        kind = 'intersection';
      } else if (current('-')) {
        kind = 'subtraction';
      } else {
        kind = 'union';
      }

      while (!current(']')) {
        if (kind === 'intersection') {
          skip('&');
          skip('&');
          if (current('&')) {
            bail('&& cannot be followed by &. Wrap it in parentheses: &&(&).');
          }
        } else if (kind === 'subtraction') {
          skip('-');
          skip('-');
        }

        operand = parseClassOperand(/* allowRanges*/ kind === 'union');
        body.push(operand);
      }

      return { kind: kind, body: body };
    }

    function parseClassOperand(allowRanges) {
      // ClassOperand ::
      //      ClassCharacter
      //      ClassStrings
      //      NestedClass
      //
      // NestedClass ::
      //      [ [lookahead ≠ ^] ClassRanges[+U,+V] ]
      //      [ ^ ClassRanges[+U,+V] ]
      //      \ CharacterClassEscape[+U, +V]
      //
      // ClassRange ::
      //      ClassCharacter - ClassCharacter
      //
      // ClassCharacter ::
      //      [lookahead ∉ ClassReservedDouble] SourceCharacter but not ClassSyntaxCharacter
      //      \ CharacterEscape[+U]
      //      \ ClassHalfOfDouble
      //      \ b
      //
      // ClassSyntaxCharacter ::
      //      one of ( ) [ ] { } / - \ |

      var from = pos;
      var start, res;

      if (match('\\')) {
        if (res = parseCharacterClassEscape()) {
          start = res;
        } else if (res = parseClassCharacterEscapedHelper()) {
          // ClassOperand ::
          //      ...
          //      NestedClass
          //
          // NestedClass ::
          //      ...
          //      \ CharacterClassEscape[+U, +V]
          return res;
        } else {
          bail('Invalid escape', '\\' + lookahead(), from);
        }
      } else if (res = parseClassCharacterUnescapedHelper()) {
        start = res;
      } else if (res = parseClassStrings() || parseCharacterClass()) {
        // ClassOperand ::
        //      ...
        //      ClassStrings
        //      NestedClass
        //
        // NestedClass ::
        //      [ [lookahead ≠ ^] ClassRanges[+U,+V] ]
        //      [ ^ ClassRanges[+U,+V] ]
        //      ...
        return res;
      } else {
        bail('Invalid character', lookahead());
      }

      if (allowRanges && current('-') && !next('-')) {
        skip('-');

        if (res = parseClassCharacter()) {
          // ClassRange ::
          //      ClassCharacter - ClassCharacter
          return createClassRange(start, res, from, pos);
        }

        bail('Invalid range end', lookahead());
      }

      // ClassOperand ::
      //      ClassCharacter
      //      ...
      return start;
    }

    function parseClassCharacter() {
      // ClassCharacter ::
      //      [lookahead ∉ ClassReservedDouble] SourceCharacter but not ClassSyntaxCharacter
      //      \ CharacterEscape[+U]
      //      \ ClassHalfOfDouble
      //      \ b

      if (match('\\')) {
        if (res = parseClassCharacterEscapedHelper()) {
          return res;
        } else {
          bail('Invalid escape', '\\' + lookahead(), from);
        }
      }

      return parseClassCharacterUnescapedHelper();
    }

    function parseClassCharacterUnescapedHelper() {
      // ClassCharacter ::
      //      [lookahead ∉ ClassReservedDouble] SourceCharacter but not ClassSyntaxCharacter
      //      ...

      var res;
      if (res = matchReg(/^[^()[\]{}/\-\\|]/)) {
        return createCharacter(res);
      };
    }

    function parseClassCharacterEscapedHelper() {
      // ClassCharacter ::
      //      ...
      //      \ CharacterEscape[+U]
      //      \ ClassHalfOfDouble
      //      \ b

      if (match('b')) {
        return createEscaped('singleEscape', 0x0008, '\\b');
      } else if (match('B')) {
        bail('\\B not possible inside of ClassContents', '', pos - 2);
      } else if (res = matchReg(/^[&\-!#%,:;<=>@_`~]/)) {
        return createEscaped('identifier', res[0].codePointAt(0), res[0]);
      } else if (res = parseCharacterEscape()) {
        return res;
      } else {
        return null;
      }
    }

    function parseClassStrings() {
      // ClassStrings ::
      //      ( ClassString MoreClassStrings? )

      var res = [];
      var from = pos;

      if (!match('(')) {
        return null;
      }

      do {
        res.push(parseClassString());
      } while (match('|'));

      skip(')');

      return createClassStrings(res, from, pos);
    }

    function parseClassString() {
      // ClassString ::
      //      [empty]
      //      NonEmptyClassString
      //
      // NonEmptyClassString ::
      //      ClassCharacter NonEmptyClassString?

      var res = [], from = pos;
      var char;

      while (char = parseClassCharacter()) {
        res.push(char);
      }

      return createClassString(res, from, pos);
    }

    function bail(message, details, from, to) {
      from = from == null ? pos : from;
      to = to == null ? from : to;

      var contextStart = Math.max(0, from - 10);
      var contextEnd = Math.min(to + 10, str.length);

      // Output a bit of context and a line pointing to where our error is.
      //
      // We are assuming that there are no actual newlines in the content as this is a regular expression.
      var context = '    ' + str.substring(contextStart, contextEnd);
      var pointer = '    ' + new Array(from - contextStart + 1).join(' ') + '^';

      throw SyntaxError(message + ' at position ' + from + (details ? ': ' + details : '') + '\n' + context + '\n' + pointer);
    }

    var backrefDenied = [];
    var closedCaptureCounter = 0;
    var firstIteration = true;
    var hasUnicodeFlag = (flags || "").indexOf("u") !== -1;
    var hasUnicodeSetFlag = (flags || "").indexOf("v") !== -1;
    var pos = 0;

    if (hasUnicodeSetFlag && !features.unicodeSet) {
      throw new Error('The "v" flag is only supported when the .unicodeSet option is enabled.');
    }

    if (hasUnicodeFlag && hasUnicodeSetFlag) {
      throw new Error('The "u" and "v" flags are mutually exclusive.');
    }

    // Convert the input to a string and treat the empty string special.
    str = String(str);
    if (str === '') {
      str = '(?:)';
    }

    var result = parseDisjunction();

    if (result.range[1] !== str.length) {
      bail('Could not parse entire input - got stuck', '', result.range[1]);
    }

    // The spec requires to interpret the `\2` in `/\2()()/` as backreference.
    // As the parser collects the number of capture groups as the string is
    // parsed it is impossible to make these decisions at the point when the
    // `\2` is handled. In case the local decision turns out to be wrong after
    // the parsing has finished, the input string is parsed a second time with
    // the total number of capture groups set.
    //
    // SEE: https://github.com/jviereck/regjsparser/issues/70
    for (var i = 0; i < backrefDenied.length; i++) {
      if (backrefDenied[i] <= closedCaptureCounter) {
        // Parse the input a second time.
        pos = 0;
        firstIteration = false;
        return parseDisjunction();
      }
    }

    return result;
  }

  var regjsparser = {
    parse: parse
  };

  if (typeof module !== 'undefined' && module.exports) {
    module.exports = regjsparser;
  } else {
    window.regjsparser = regjsparser;
  }

}());