/*
 * Copyright (C) 2007-2019 Diego Perini
 * All rights reserved.
 *
 * nwsapi.js - Fast CSS Selectors API Engine
 *
 * Author: Diego Perini <diego.perini at gmail com>
 * Version: 2.1.4
 * Created: 20070722
 * Release: 20190426
 *
 * License:
 *  http://javascript.nwbox.com/nwsapi/MIT-LICENSE
 * Download:
 *  http://javascript.nwbox.com/nwsapi/nwsapi.js
 */

(function Export(global, factory) {

  'use strict';

  if (typeof module == 'object' && typeof exports == 'object') {
    module.exports = factory;
  } else if (typeof define == 'function' && define['amd']) {
    define(factory);
  } else {
    global.NW || (global.NW = { });
    global.NW.Dom = factory(global, Export);
  }

})(this, function Factory(global, Export) {

  var version = 'nwsapi-2.1.4',

  doc = global.document,
  root = doc.documentElement,

  WSP = '[\\x20\\t\\r\\n\\f]',

  CFG = {
    // extensions
    operators: '[~*^$|]=|=',
    combinators: '[\\x20\\t>+~](?=[^>+~])'
  },

  NOT = {
    // not enclosed in double/single/parens/square
    double_enc: '(?=(?:[^"]*["][^"]*["])*[^"]*$)',
    single_enc: "(?=(?:[^']*['][^']*['])*[^']*$)",
    parens_enc: '(?![^\\x28]*\\x29)',
    square_enc: '(?![^\\x5b]*\\x5d)'
  },

  REX = {
    // regular expressions
    HasEscapes: RegExp('\\\\'),
    HexNumbers: RegExp('^[0-9a-fA-F]'),
    EscOrQuote: RegExp('^\\\\|[\\x22\\x27]'),
    RegExpChar: RegExp('(?:(?!\\\\)[\\\\^$.*+?()[\\]{}|\\/])', 'g'),
    TrimSpaces: RegExp('[\\r\\n\\f]|^' + WSP + '+|' + WSP + '+$', 'g'),
    CommaGroup: RegExp('(\\s*,\\s*)' + NOT.square_enc + NOT.parens_enc, 'g'),
    SplitGroup: RegExp('((?:\\x28[^\\x29]*\\x29|\\[[^\\]]*\\]|\\\\.|[^,])+)', 'g'),
    FixEscapes: RegExp('\\\\([0-9a-fA-F]{1,6}' + WSP + '?|.)|([\\x22\\x27])', 'g'),
    CombineWSP: RegExp('[\\n\\r\\f\\x20]+' + NOT.single_enc + NOT.double_enc, 'g'),
    TabCharWSP: RegExp('(\\x20?\\t+\\x20?)' + NOT.single_enc + NOT.double_enc, 'g'),
    PseudosWSP: RegExp('\\s+([-+])\\s+' + NOT.square_enc, 'g')
  },

  STD = {
    combinator: RegExp('\\s?([>+~])\\s?', 'g'),
    apimethods: RegExp('^(?:[a-z]+|\\*)\\|', 'i'),
    namespaces: RegExp('(\\*|[a-z]+)\\|[-a-z]+', 'i')
  },

  GROUPS = {
    // pseudo-classes requiring parameters
    linguistic: '(dir|lang)\\x28\\s?([-\\w]{2,})\\s?(?:\\x29|$)',
    logicalsel: '(matches|not)\\x28\\s?([^()]*|[^\\x28]*\\x28[^\\x29]*\\x29)\\s?(?:\\x29|$)',
    treestruct: '(nth(?:-last)?(?:-child|-of-type))(?:\\x28\\s?(even|odd|(?:[-+]?\\d*)(?:n\\s?[-+]?\\s?\\d*)?)\\s?(?:\\x29|$))',
    // pseudo-classes not requiring parameters
    locationpc: '(link|visited|target)\\b',
    useraction: '(hover|active|focus|focus-within)\\b',
    structural: '(root|empty|(?:(?:first|last|only)(?:-child|-of-type)))\\b',
    inputstate: '(enabled|disabled|read-only|read-write|placeholder-shown|default)\\b',
    inputvalue: '(checked|indeterminate|required|optional|valid|invalid|in-range|out-of-range)\\b',
    pseudo_dbl: '(after|before|first-letter|first-line|-webkit-[-a-zA-Z0-9]{2,})\\b',
    pseudo_sng: ':(after|before|first-letter|first-line|selection|placeholder)\\b'
  },

  Patterns = {
    // pseudo-classes
    treestruct: RegExp('^:(?:' + GROUPS.treestruct + ')(.*)', 'i'),
    structural: RegExp('^:(?:' + GROUPS.structural + ')(.*)', 'i'),
    linguistic: RegExp('^:(?:' + GROUPS.linguistic + ')(.*)', 'i'),
    useraction: RegExp('^:(?:' + GROUPS.useraction + ')(.*)', 'i'),
    inputstate: RegExp('^:(?:' + GROUPS.inputstate + ')(.*)', 'i'),
    inputvalue: RegExp('^:(?:' + GROUPS.inputvalue + ')(.*)', 'i'),
    locationpc: RegExp('^:(?:' + GROUPS.locationpc + ')(.*)', 'i'),
    logicalsel: RegExp('^:(?:' + GROUPS.logicalsel + ')(.*)', 'i'),
    pseudo_dbl: RegExp('^:(?:' + GROUPS.pseudo_dbl + ')(.*)', 'i'),
    pseudo_sng: RegExp('^:(?:' + GROUPS.pseudo_sng + ')(.*)', 'i'),
    // combinators symbols
    children: RegExp('^' + WSP + '?\\>' + WSP + '?(.*)'),
    adjacent: RegExp('^' + WSP + '?\\+' + WSP + '?(.*)'),
    relative: RegExp('^' + WSP + '?\\~' + WSP + '?(.*)'),
    ancestor: RegExp('^' + WSP + '+(.*)'),
   // universal & namespace
   universal: RegExp('^\\*(.*)'),
   namespace: RegExp('^(\\w+|\\*)?\\|(.*)')
  },

  // regexp to aproximate detection of RTL languages (Arabic)
  RTL = RegExp('^[\\u0591-\\u08ff\\ufb1d-\\ufdfd\\ufe70-\\ufefc ]+$'),

  // emulate firefox error strings
  qsNotArgs = 'Not enough arguments',
  qsInvalid = ' is not a valid selector',

  // detect structural pseudo-classes in selectors
  reNthElem = RegExp('(:nth(?:-last)?-child)', 'i'),
  reNthType = RegExp('(:nth(?:-last)?-of-type)', 'i'),

  // placeholder for global regexp
  reOptimizer,
  reValidator,

  // special handling configuration flags
  Config = {
    IDS_DUPES: true,
    LIVECACHE: false,
    MIXEDCASE: true,
    LOGERRORS: true,
    VERBOSITY: true
  },

  NAMESPACE,
  QUIRKS_MODE,
  HTML_DOCUMENT,

  ATTR_STD_OPS = {
    '=': 1, '^=': 1, '$=': 1, '|=': 1, '*=': 1, '~=': 1
  },

  HTML_TABLE = {
    'accept': 1, 'accept-charset': 1, 'align': 1, 'alink': 1, 'axis': 1,
    'bgcolor': 1, 'charset': 1, 'checked': 1, 'clear': 1, 'codetype': 1, 'color': 1,
    'compact': 1, 'declare': 1, 'defer': 1, 'dir': 1, 'direction': 1, 'disabled': 1,
    'enctype': 1, 'face': 1, 'frame': 1, 'hreflang': 1, 'http-equiv': 1, 'lang': 1,
    'language': 1, 'link': 1, 'media': 1, 'method': 1, 'multiple': 1, 'nohref': 1,
    'noresize': 1, 'noshade': 1, 'nowrap': 1, 'readonly': 1, 'rel': 1, 'rev': 1,
    'rules': 1, 'scope': 1, 'scrolling': 1, 'selected': 1, 'shape': 1, 'target': 1,
    'text': 1, 'type': 1, 'valign': 1, 'valuetype': 1, 'vlink': 1
  },

  Combinators = { },

  Selectors = { },

  Operators = {
     '=': { p1: '^',
            p2: '$',
            p3: 'true' },
    '^=': { p1: '^',
            p2: '',
            p3: 'true' },
    '$=': { p1: '',
            p2: '$',
            p3: 'true' },
    '*=': { p1: '',
            p2: '',
            p3: 'true' },
    '|=': { p1: '^',
            p2: '(-|$)',
            p3: 'true' },
    '~=': { p1: '(^|\\s)',
            p2: '(\\s|$)',
            p3: 'true' }
  },

  concatCall =
    function(nodes, callback) {
      var i = 0, l = nodes.length, list = Array(l);
      while (l > i) {
        if (false === callback(list[i] = nodes[i])) break;
        ++i;
      }
      return list;
    },

  concatList =
    function(list, nodes) {
      var i = -1, l = nodes.length;
      while (l--) { list[list.length] = nodes[++i]; }
      return list;
    },

  documentOrder =
    function(a, b) {
      if (!hasDupes && a === b) {
        hasDupes = true;
        return 0;
      }
      return a.compareDocumentPosition(b) & 4 ? -1 : 1;
    },

  hasDupes = false,

  unique =
    function(nodes) {
      var i = 0, j = -1, l = nodes.length + 1, list = [ ];
      while (--l) {
        if (nodes[i++] === nodes[i]) continue;
        list[++j] = nodes[i - 1];
      }
      hasDupes = false;
      return list;
    },

  // check context for mixed content
  hasMixedCaseTagNames =
    function(context) {
      var ns, api = 'getElementsByTagNameNS';

      // current host context (ownerDocument)
      context = context.ownerDocument || context;

      // documentElement (root) element namespace or default html/xhtml namespace
      ns = context.documentElement.namespaceURI || 'http://www.w3.org/1999/xhtml';

      // checking the number of non HTML nodes in the document
      return (context[api]('*', '*').length - context[api](ns, '*').length) > 0;
    },

  switchContext =
    function(context, force) {
      var oldDoc = doc;
      doc = context.ownerDocument || context;
      if (force || oldDoc !== doc) {
        // force a new check for each document change
        // performed before the next select operation
        root = doc.documentElement;
        HTML_DOCUMENT = isHTML(doc);
        QUIRKS_MODE = HTML_DOCUMENT &&
          doc.compatMode.indexOf('CSS') < 0;
        NAMESPACE = root && root.namespaceURI;
        Snapshot.doc = doc;
        Snapshot.root = root;
      }
      return (Snapshot.from = context);
    },

  // convert single codepoint to UTF-16 encoding
  codePointToUTF16 =
    function(codePoint) {
      // out of range, use replacement character
      if (codePoint < 1 || codePoint > 0x10ffff ||
        (codePoint > 0xd7ff && codePoint < 0xe000)) {
        return '\\ufffd';
      }
      // javascript strings are UTF-16 encoded
      if (codePoint < 0x10000) {
        var lowHex = '000' + codePoint.toString(16);
        return '\\u' + lowHex.substr(lowHex.length - 4);
      }
      // supplementary high + low surrogates
      return '\\u' + (((codePoint - 0x10000) >> 0x0a) + 0xd800).toString(16) +
             '\\u' + (((codePoint - 0x10000) % 0x400) + 0xdc00).toString(16);
    },

  // convert single codepoint to string
  stringFromCodePoint =
    function(codePoint) {
      // out of range, use replacement character
      if (codePoint < 1 || codePoint > 0x10ffff ||
        (codePoint > 0xd7ff && codePoint < 0xe000)) {
        return '\ufffd';
      }
      if (codePoint < 0x10000) {
        return String.fromCharCode(codePoint);
      }
      return String.fromCodePoint ?
        String.fromCodePoint(codePoint) :
        String.fromCharCode(
          ((codePoint - 0x10000) >> 0x0a) + 0xd800,
          ((codePoint - 0x10000) % 0x400) + 0xdc00);
    },

  // convert escape sequence in a CSS string or identifier
  // to javascript string with javascript escape sequences
  convertEscapes =
    function(str) {
      return REX.HasEscapes.test(str) ?
        str.replace(REX.FixEscapes,
          function(substring, p1, p2) {
            // unescaped " or '
            return p2 ? '\\' + p2 :
              // javascript strings are UTF-16 encoded
              REX.HexNumbers.test(p1) ? codePointToUTF16(parseInt(p1, 16)) :
              // \' \"
              REX.EscOrQuote.test(p1) ? substring :
              // \g \h \. \# etc
              p1;
          }
        ) : str;
    },

  // convert escape sequence in a CSS string or identifier
  // to javascript string with characters representations
  unescapeIdentifier =
    function(str) {
      return REX.HasEscapes.test(str) ?
        str.replace(REX.FixEscapes,
          function(substring, p1, p2) {
            // unescaped " or '
            return p2 ? p2 :
              // javascript strings are UTF-16 encoded
              REX.HexNumbers.test(p1) ? stringFromCodePoint(parseInt(p1, 16)) :
              // \' \"
              REX.EscOrQuote.test(p1) ? substring :
              // \g \h \. \# etc
              p1;
          }
        ) : str;
    },

  method = {
    '#': 'getElementById',
    '*': 'getElementsByTagName',
    '.': 'getElementsByClassName'
    },

  compat = {
    '#': function(c, n) { REX.HasEscapes.test(n) && (n = unescapeIdentifier(n)); return function(e, f) { return byId(n, c); }; },
    '*': function(c, n) { REX.HasEscapes.test(n) && (n = unescapeIdentifier(n)); return function(e, f) { return byTag(n, c); }; },
    '.': function(c, n) { REX.HasEscapes.test(n) && (n = unescapeIdentifier(n)); return function(e, f) { return byClass(n, c); }; }
    },

  // find duplicate ids using iterative walk
  byIdRaw =
    function(id, context) {
      var node = context, nodes = [ ], next = node.firstElementChild;
      while ((node = next)) {
        node.id == id && (nodes[nodes.length] = node);
        if ((next = node.firstElementChild || node.nextElementSibling)) continue;
        while (!next && (node = node.parentElement) && node !== context) {
          next = node.nextElementSibling;
        }
      }
      return nodes;
    },

  // context agnostic getElementById
  byId =
    function(id, context) {
      var e, nodes, api = method['#'];

      // duplicates id allowed
      if (Config.IDS_DUPES === false) {
        if (api in context) {
          return (e = context[api](id)) ? [ e ] : none;
        }
      } else {
        if ('all' in context) {
          if ((e = context.all[id])) {
            if (e.nodeType == 1) return e.getAttribute('id') != id ? [ ] : [ e ];
            else if (id == 'length') return (e = context[api](id)) ? [ e ] : none;
            for (i = 0, l = e.length, nodes = [ ]; l > i; ++i) {
              if (e[i].id == id) nodes[nodes.length] = e[i];
            }
            return nodes && nodes.length ? nodes : [ nodes ];
          } else return none;
        }
      }

      return byIdRaw(id, context);
    },

  // context agnostic getElementsByTagName
  byTag =
    function(tag, context) {
      var e, nodes, api = method['*'];
      // DOCUMENT_NODE (9) & ELEMENT_NODE (1)
      if (api in context) {
        return context[api](tag);
      } else {
        // DOCUMENT_FRAGMENT_NODE (11)
        if ((e = context.firstElementChild)) {
          tag = tag.toLowerCase();
          if (!(e.nextElementSibling || tag == '*' || e.nodeName.toLowerCase() == tag)) {
            return e[api](tag);
          } else {
            nodes = [ ];
            do {
              if (tag == '*' || e.nodeName.toLowerCase() == tag) nodes[nodes.length] = e;
              concatList(nodes, e[api](tag));
            } while ((e = e.nextElementSibling));
          }
        } else nodes = none;
      }
      return nodes;
    },

  // context agnostic getElementsByClassName
  byClass =
    function(cls, context) {
      var e, nodes, api = method['.'], reCls;
      // DOCUMENT_NODE (9) & ELEMENT_NODE (1)
      if (api in context) {
        return context[api](cls);
      } else {
        // DOCUMENT_FRAGMENT_NODE (11)
        if ((e = context.firstElementChild)) {
          reCls = RegExp('(^|\\s)' + cls + '(\\s|$)', QUIRKS_MODE ? 'i' : '');
          if (!(e.nextElementSibling || reCls.test(e.className))) {
            return e[api](cls);
          } else {
            nodes = [ ];
            do {
              if (reCls.test(e.className)) nodes[nodes.length] = e;
              concatList(nodes, e[api](cls));
            } while ((e = e.nextElementSibling));
          }
        } else nodes = none;
      }
      return nodes;
    },

  // namespace aware hasAttribute
  // helper for XML/XHTML documents
  hasAttributeNS =
    function(e, name) {
      var i, l, attr = e.getAttributeNames();
      HTML_DOCUMENT && (name = name.toLowerCase());
      for (i = 0, l = attr.length; l > i; ++i) {
        if (name == attr[i].toLowerCase()) return true;
      }
      return false;
    },

  // fast resolver for the :nth-child() and :nth-last-child() pseudo-classes
  nthElement = (function() {
    var idx = 0, len = 0, set = 0, parent = undefined, parents = Array(), nodes = Array();
    return function(element, dir) {
      // ensure caches are emptied after each run, invoking with dir = 2
      if (dir == 2) {
        idx = 0; len = 0; set = 0; nodes.length = 0;
        parents.length = 0; parent = undefined;
        return -1;
      }
      var e, i, j, k, l;
      if (parent === element.parentElement) {
        i = set; j = idx; l = len;
      } else {
        l = parents.length;
        parent = element.parentElement;
        for (i = -1, j = 0, k = l - 1; l > j; ++j, --k) {
          if (parents[j] === parent) { i = j; break; }
          if (parents[k] === parent) { i = k; break; }
        }
        if (i < 0) {
          parents[i = l] = parent;
          l = 0; nodes[i] = Array();
          e = parent && parent.firstElementChild || element;
          while (e) { nodes[i][l] = e; if (e === element) j = l; e = e.nextElementSibling; ++l; }
          set = i; idx = 0; len = l;
          if (l < 2) return l;
        } else {
          l = nodes[i].length;
          set = i;
        }
      }
      if (element !== nodes[i][j] && element !== nodes[i][j = 0]) {
        for (j = 0, e = nodes[i], k = l - 1; l > j; ++j, --k) {
          if (e[j] === element) { break; }
          if (e[k] === element) { j = k; break; }
        }
      }
      idx = j + 1; len = l;
      return dir ? l - j : idx;
    };
  })(),

  // fast resolver for the :nth-of-type() and :nth-last-of-type() pseudo-classes
  nthOfType = (function() {
    var idx = 0, len = 0, set = 0, parent = undefined, parents = Array(), nodes = Array();
    return function(element, dir) {
      // ensure caches are emptied after each run, invoking with dir = 2
      if (dir == 2) {
        idx = 0; len = 0; set = 0; nodes.length = 0;
        parents.length = 0; parent = undefined;
        return -1;
      }
      var e, i, j, k, l, name = element.nodeName;
      if (nodes[set] && nodes[set][name] && parent === element.parentElement) {
        i = set; j = idx; l = len;
      } else {
        l = parents.length;
        parent = element.parentElement;
        for (i = -1, j = 0, k = l - 1; l > j; ++j, --k) {
          if (parents[j] === parent) { i = j; break; }
          if (parents[k] === parent) { i = k; break; }
        }
        if (i < 0 || !nodes[i][name]) {
          parents[i = l] = parent;
          nodes[i] || (nodes[i] = Object());
          l = 0; nodes[i][name] = Array();
          e = parent && parent.firstElementChild || element;
          while (e) { if (e === element) j = l; if (e.nodeName == name) { nodes[i][name][l] = e; ++l; } e = e.nextElementSibling; }
          set = i; idx = j; len = l;
          if (l < 2) return l;
        } else {
          l = nodes[i][name].length;
          set = i;
        }
      }
      if (element !== nodes[i][name][j] && element !== nodes[i][name][j = 0]) {
        for (j = 0, e = nodes[i][name], k = l - 1; l > j; ++j, --k) {
          if (e[j] === element) { break; }
          if (e[k] === element) { j = k; break; }
        }
      }
      idx = j + 1; len = l;
      return dir ? l - j : idx;
    };
  })(),

  // check if the document type is HTML
  isHTML =
    function(node) {
      var doc = node.ownerDocument || node;
      return doc.nodeType == 9 &&
        // contentType not in IE <= 11
        'contentType' in doc ?
          doc.contentType.indexOf('/html') > 0 :
          doc.createElement('DiV').nodeName == 'DIV';
    },

  // configure the engine to use special handling
  configure =
    function(option, clear) {
      if (typeof option == 'string') { return !!Config[option]; }
      if (typeof option != 'object') { return Config; }
      for (var i in option) {
        Config[i] = !!option[i];
      }
      // clear lambda cache
      if (clear) {
        matchResolvers = { };
        selectResolvers = { };
      }
      setIdentifierSyntax();
      return true;
    },

  // centralized error and exceptions handling
  emit =
    function(message, proto) {
      var err;
      if (Config.VERBOSITY) {
        if (proto) {
          err = new proto(message);
        } else {
          err = new global.DOMException(message, 'SyntaxError');
        }
        throw err;
      }
      if (Config.LOGERRORS && console && console.log) {
        console.log(message);
      }
    },

  // execute the engine initialization code
  initialize =
    function(doc) {
      setIdentifierSyntax();
      lastContext = switchContext(doc, true);
    },

  // build validation regexps used by the engine
  setIdentifierSyntax =
    function() {

      //
      // NOTE: SPECIAL CASES IN CSS SYNTAX PARSING RULES
      //
      // The <EOF-token> https://drafts.csswg.org/css-syntax/#typedef-eof-token
      // allow mangled|unclosed selector syntax at the end of selectors strings
      //
      // Literal equivalent hex representations of the characters: " ' ` ] )
      //
      //     \\x22 = " - double quotes    \\x5b = [ - open square bracket
      //     \\x27 = ' - single quote     \\x5d = ] - closed square bracket
      //     \\x60 = ` - back tick        \\x28 = ( - open round parens
      //     \\x5c = \ - back slash       \\x29 = ) - closed round parens
      //
      // using hex format prevents false matches of opened/closed instances
      // pairs, coloring breakage and other editors highlightning problems.
      //

      var identifier =
        // doesn't start with a digit
        '(?=[^0-9])' +
        // can start with double dash
        '(?:-{2}' +
          // may include ascii chars
          '|[a-zA-Z0-9-_]' +
          // non-ascii chars
          '|[^\\x00-\\x9f]' +
          // escaped chars
          '|\\\\[^\\r\\n\\f0-9a-fA-F]' +
          // unicode chars
          '|\\\\[0-9a-fA-F]{1,6}(?:\\r\\n|\\s)?' +
          // any escaped chars
          '|\\\\.' +
        ')+',

      pseudonames = '[-\\w]+',
      pseudoparms = '(?:[-+]?\\d*)(?:n\\s?[-+]?\\s?\\d*)',
      doublequote = '"[^"\\\\]*(?:\\\\.[^"\\\\]*)*(?:"|$)',
      singlequote = "'[^'\\\\]*(?:\\\\.[^'\\\\]*)*(?:'|$)",

      attrparser = identifier + '|' + doublequote + '|' + singlequote,

      attrvalues = '([\\x22\\x27]?)((?!\\3)*|(?:\\\\?.)*?)(?:\\3|$)',

      attributes =
        '\\[' +
          // attribute presence
          '(?:\\*\\|)?' +
          WSP + '?' +
          '(' + identifier + '(?::' + identifier + ')?)' +
          WSP + '?' +
          '(?:' +
            '(' + CFG.operators + ')' + WSP + '?' +
            '(?:' + attrparser + ')' +
          ')?' +
          // attribute case sensitivity
          WSP + '?' + '(i)?' + WSP + '?' +
        '(?:\\]|$)',

      attrmatcher = attributes.replace(attrparser, attrvalues),

      pseudoclass =
        '(?:\\x28' + WSP + '*' +
          '(?:' + pseudoparms + '?)?|' +
          // universal * &
          // namespace *|*
          '(?:\\*|\\|)|' +
          '(?:' +
            '(?::' + pseudonames +
            '(?:\\x28' + pseudoparms + '?(?:\\x29|$))?|' +
          ')|' +
          '(?:[.#]?' + identifier + ')|' +
          '(?:' + attributes + ')' +
          ')+|' +
          '(?:' + WSP + '?,' + WSP + '?)|' +
          '(?:' + WSP + '?)|' +
          '(?:\\x29|$))*',

      standardValidator =
        '(?=' + WSP + '?[^>+~(){}<>])' +
        '(?:' +
          // universal * &
          // namespace *|*
          '(?:\\*|\\|)|' +
          '(?:[.#]?' + identifier + ')+|' +
          '(?:' + attributes + ')+|' +
          '(?:::?' + pseudonames + pseudoclass + ')|' +
          '(?:' + WSP + '?' + CFG.combinators + WSP + '?)|' +
          '(?:' + WSP + '?,' + WSP + '?)|' +
          '(?:' + WSP + '?)' +
        ')+';

      // the following global RE is used to return the
      // deepest nodeName in selector strings and then
      // use it to retrieve all possible matching nodes
      // that will be filtered by compiled resolvers
      reOptimizer = RegExp(
        '(?:([.:#*]?)' +
        '(' + identifier + ')' +
        '(?:' +
          ':[-\\w]+|' +
          '\\[[^\\]]+(?:\\]|$)|' +
          '\\x28[^\\x29]+(?:\\x29|$)' +
        ')*)$');

      // global
      reValidator = RegExp(standardValidator, 'g');

      Patterns.id = RegExp('^#(' + identifier + ')(.*)');
      Patterns.tagName = RegExp('^(' + identifier + ')(.*)');
      Patterns.className = RegExp('^\\.(' + identifier + ')(.*)');
      Patterns.attribute = RegExp('^(?:' + attrmatcher + ')(.*)');
    },

  F_INIT = '"use strict";return function Resolver(c,f,x,r)',

  S_HEAD = 'var e,n,o,j=r.length-1,k=-1',
  M_HEAD = 'var e,n,o',

  S_LOOP = 'main:while((e=c[++k]))',
  N_LOOP = 'main:while((e=c.item(++k)))',
  M_LOOP = 'e=c;',

  S_BODY = 'r[++j]=c[k];',
  N_BODY = 'r[++j]=c.item(k);',
  M_BODY = '',

  S_TAIL = 'continue main;',
  M_TAIL = 'r=true;',

  S_TEST = 'if(f(c[k])){break main;}',
  N_TEST = 'if(f(c.item(k))){break main;}',
  M_TEST = 'f(c);',

  S_VARS = [ ],
  M_VARS = [ ],

  // compile groups or single selector strings into
  // executable functions for matching or selecting
  compile =
    function(selector, mode, callback) {
      var factory, token, head = '', loop = '', macro = '', source = '', vars = '';

      // 'mode' can be boolean or null
      // true = select / false = match
      // null to use collection.item()
      switch (mode) {
        case true:
          if (selectLambdas[selector]) { return selectLambdas[selector]; }
          macro = S_BODY + (callback ? S_TEST : '') + S_TAIL;
          head = S_HEAD;
          loop = S_LOOP;
          break;
        case false:
          if (matchLambdas[selector]) { return matchLambdas[selector]; }
          macro = M_BODY + (callback ? M_TEST : '') + M_TAIL;
          head = M_HEAD;
          loop = M_LOOP;
          break;
        case null:
          if (selectLambdas[selector]) { return selectLambdas[selector]; }
          macro = N_BODY + (callback ? N_TEST : '') + S_TAIL;
          head = S_HEAD;
          loop = N_LOOP;
          break;
        default:
          break;
      }

      source = compileSelector(selector, macro, mode, callback, false);

      loop += mode || mode === null ? '{' + source + '}' : source;

      if (mode || mode === null && selector.includes(':nth')) {
        loop += reNthElem.test(selector) ? 's.nthElement(null, 2);' : '';
        loop += reNthType.test(selector) ? 's.nthOfType(null, 2);' : '';
      }

      if (S_VARS[0] || M_VARS[0]) {
        vars = ',' + (S_VARS.join(',') || M_VARS.join(','));
        S_VARS.length = 0;
        M_VARS.length = 0;
      }

      factory = Function('s', F_INIT + '{' + head + vars + ';' + loop + 'return r;}')(Snapshot);

      return mode || mode === null ? (selectLambdas[selector] = factory) : (matchLambdas[selector] = factory);
    },

  // build conditional code to check components of selector strings
  compileSelector =
    function(expression, source, mode, callback, not) {

      // N is the negation pseudo-class flag
      // D is the default inverted negation flag
      var a, b, n, f, i, l, name, nested, NS,
      N = not ? '!' : '', D = not ? '' : '!',
      compat, expr, match, result, status, symbol, test,
      type, selector = expression, selector_string, vars;

      // original 'select' or 'match' selector string before normalization
      selector_string = mode ? lastSelected : lastMatched;

      // isolate selector combinators/components and normalize whitespace
      selector = selector.replace(STD.combinator, '$1');//.replace(STD.whitespace, ' ');

      while (selector) {

        // get namespace prefix if present or get first char of selector
        symbol = STD.apimethods.test(selector) ? '|' : selector[0];

        switch (symbol) {

          // universal resolver
          case '*':
            match = selector.match(Patterns.universal);
            if (N == '!') {
              source = 'if(' + N + 'true' +
                '){' + source + '}';
            }
            break;

          // id resolver
          case '#':
            match = selector.match(Patterns.id);
            source = 'if(' + N + '(/^' + match[1] + '$/.test(e.getAttribute("id"))' +
              ')){' + source + '}';
            break;

          // class name resolver
          case '.':
            match = selector.match(Patterns.className);
            compat = (QUIRKS_MODE ? 'i' : '') + '.test(e.getAttribute("class"))';
            source = 'if(' + N + '(/(^|\\s)' + match[1] + '(\\s|$)/' + compat +
              ')){' + source + '}';
            break;

          // tag name resolver
          case (/[a-z]/i.test(symbol) ? symbol : undefined):
            match = selector.match(Patterns.tagName);
            source = 'if(' + N + '(e.nodeName' +
              (Config.MIXEDCASE || hasMixedCaseTagNames(doc) ?
                '.toLowerCase()=="' + match[1].toLowerCase() + '"' :
                '=="' + match[1].toUpperCase() + '"') +
              ')){' + source + '}';
            break;

          // namespace resolver
          case '|':
            match = selector.match(Patterns.namespace);
            if (match[1] == '*') {
              source = 'if(' + N + 'true){' + source + '}';
            } else if (!match[1]) {
              source = 'if(' + N + '(!e.namespaceURI)){' + source + '}';
            } else if (typeof match[1] == 'string' && root.prefix == match[1]) {
              source = 'if(' + N + '(e.namespaceURI=="' + NAMESPACE + '")){' + source + '}';
            } else {
              emit('\'' + selector_string + '\'' + qsInvalid);
            }
            break;

          // attributes resolver
          case '[':
            match = selector.match(Patterns.attribute);
            NS = match[0].match(STD.namespaces);
            name = match[1];
            expr = name.split(':');
            expr = expr.length == 2 ? expr[1] : expr[0];
            if (match[2] && !(test = Operators[match[2]])) {
              emit('\'' + selector_string + '\'' + qsInvalid);
              return '';
            }
            if (match[4] === '') {
              test = match[2] == '~=' ?
                { p1: '^\\s', p2: '+$', p3: 'true' } :
                  match[2] in ATTR_STD_OPS && match[2] != '~=' ?
                { p1: '^',    p2: '$',  p3: 'true' } : test;
            } else if (match[2] == '~=' && match[4].includes(' ')) {
              // whitespace separated list but value contains space
              source = 'if(' + N + 'false){' + source + '}';
              break;
            } else if (match[4]) {
              match[4] = convertEscapes(match[4]).replace(REX.RegExpChar, '\\$&');
            }
            type = match[5] == 'i' || (HTML_DOCUMENT && HTML_TABLE[expr.toLowerCase()]) ? 'i' : '';
            source = 'if(' + N + '(' +
              (!match[2] ? (NS ? 's.hasAttributeNS(e,"' + name + '")' : 'e.hasAttribute("' + name + '")') :
              !match[4] && ATTR_STD_OPS[match[2]] && match[2] != '~=' ? 'e.getAttribute("' + name + '")==""' :
              '(/' + test.p1 + match[4] + test.p2 + '/' + type + ').test(e.getAttribute("' + name + '"))==' + test.p3) +
              ')){' + source + '}';
            break;

          // *** General sibling combinator
          // E ~ F (F relative sibling of E)
          case '~':
            match = selector.match(Patterns.relative);
            source = 'n=e;while((e=e.previousElementSibling)){' + source + '}e=n;';
            break;
          // *** Adjacent sibling combinator
          // E + F (F adiacent sibling of E)
          case '+':
            match = selector.match(Patterns.adjacent);
            source = 'n=e;if((e=e.previousElementSibling)){' + source + '}e=n;';
            break;
          // *** Descendant combinator
          // E F (E ancestor of F)
          case '\x09':
          case '\x20':
            match = selector.match(Patterns.ancestor);
            source = 'n=e;while((e=e.parentElement)){' + source + '}e=n;';
            break;
          // *** Child combinator
          // E > F (F children of E)
          case '>':
            match = selector.match(Patterns.children);
            source = 'n=e;if((e=e.parentElement)){' + source + '}e=n;';
            break;

          // *** user supplied combinators extensions
          case (symbol in Combinators ? symbol : undefined):
            // for other registered combinators extensions
            match[match.length - 1] = '*';
            source = Combinators[symbol](match) + source;
            break;

          // *** tree-structural pseudo-classes
          // :root, :empty, :first-child, :last-child, :only-child, :first-of-type, :last-of-type, :only-of-type
          case ':':
            if ((match = selector.match(Patterns.structural))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'root':
                  // there can only be one :root element, so exit the loop once found
                  source = 'if(' + N + '(e===s.root)){' + source + (mode ? 'break main;' : '') + '}';
                  break;
                case 'empty':
                  // matches elements that don't contain elements or text nodes
                  source = 'n=e.firstChild;while(n&&!(/1|3/).test(n.nodeType)){n=n.nextSibling}if(' + D + 'n){' + source + '}';
                  break;

                // *** child-indexed pseudo-classes
                // :first-child, :last-child, :only-child
                case 'only-child':
                  source = 'if(' + N + '(!e.nextElementSibling&&!e.previousElementSibling)){' + source + '}';
                  break;
                case 'last-child':
                  source = 'if(' + N + '(!e.nextElementSibling)){' + source + '}';
                  break;
                case 'first-child':
                  source = 'if(' + N + '(!e.previousElementSibling)){' + source + '}';
                  break;

                // *** typed child-indexed pseudo-classes
                // :only-of-type, :last-of-type, :first-of-type
                case 'only-of-type':
                  source = 'o=e.nodeName;' +
                    'n=e;while((n=n.nextElementSibling)&&n.nodeName!=o);if(!n){' +
                    'n=e;while((n=n.previousElementSibling)&&n.nodeName!=o);}if(' + D + 'n){' + source + '}';
                  break;
                case 'last-of-type':
                  source = 'n=e;o=e.nodeName;while((n=n.nextElementSibling)&&n.nodeName!=o);if(' + D + 'n){' + source + '}';
                  break;
                case 'first-of-type':
                  source = 'n=e;o=e.nodeName;while((n=n.previousElementSibling)&&n.nodeName!=o);if(' + D + 'n){' + source + '}';
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** child-indexed & typed child-indexed pseudo-classes
            // :nth-child, :nth-of-type, :nth-last-child, :nth-last-of-type
            else if ((match = selector.match(Patterns.treestruct))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'nth-child':
                case 'nth-of-type':
                case 'nth-last-child':
                case 'nth-last-of-type':
                  expr = /-of-type/i.test(match[1]);
                  if (match[1] && match[2]) {
                    type = /last/i.test(match[1]);
                    if (match[2] == 'n') {
                      source = 'if(' + N + 'true){' + source + '}';
                      break;
                    } else if (match[2] == '1') {
                      test = type ? 'next' : 'previous';
                      source = expr ? 'n=e;o=e.nodeName;' +
                        'while((n=n.' + test + 'ElementSibling)&&n.nodeName!=o);if(' + D + 'n){' + source + '}' :
                        'if(' + N + '!e.' + test + 'ElementSibling){' + source + '}';
                      break;
                    } else if (match[2] == 'even' || match[2] == '2n0' || match[2] == '2n+0' || match[2] == '2n') {
                      test = 'n%2==0';
                    } else if (match[2] == 'odd'  || match[2] == '2n1' || match[2] == '2n+1') {
                      test = 'n%2==1';
                    } else {
                      f = /n/i.test(match[2]);
                      n = match[2].split('n');
                      a = parseInt(n[0], 10) || 0;
                      b = parseInt(n[1], 10) || 0;
                      if (n[0] == '-') { a = -1; }
                      if (n[0] == '+') { a = +1; }
                      test = (b ? '(n' + (b > 0 ? '-' : '+') + Math.abs(b) + ')' : 'n') + '%' + a + '==0' ;
                      test =
                        a >= +1 ? (f ? 'n>' + (b - 1) + (Math.abs(a) != 1 ? '&&' + test : '') : 'n==' + a) :
                        a <= -1 ? (f ? 'n<' + (b + 1) + (Math.abs(a) != 1 ? '&&' + test : '') : 'n==' + a) :
                        a === 0 ? (n[0] ? 'n==' + b : 'n>' + (b - 1)) : 'false';
                    }
                    expr = expr ? 'OfType' : 'Element';
                    type = type ? 'true' : 'false';
                    source = 'n=s.nth' + expr + '(e,' + type + ');if(' + N + '(' + test + ')){' + source + '}';
                  } else {
                    emit('\'' + selector_string + '\'' + qsInvalid);
                  }
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** logical combination pseudo-classes
            // :matches( s1, [ s2, ... ]), :not( s1, [ s2, ... ])
            else if ((match = selector.match(Patterns.logicalsel))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'matches':
                  if (not === true || nested === true) {
                    emit(':matches() pseudo-class cannot be nested');
                  }
                  nested = true;
                  expr = match[2].replace(REX.CommaGroup, ',').replace(REX.TrimSpaces, '');
                  // check nested compound selectors s1, s2
                  expr = match[2].match(REX.SplitGroup);
                  for (i = 0, l = expr.length; l > i; ++i) {
                    expr[i] = expr[i].replace(REX.TrimSpaces, '');
                    source = 'if(s.match("' + expr[i].replace(/\x22/g, '\\"') + '",e)){' + source + '}';
                  }
                  break;
                case 'not':
                  if (not === true || nested === true) {
                    emit(':not() pseudo-class cannot be nested');
                  }
                  expr = match[2].replace(REX.CommaGroup, ',').replace(REX.TrimSpaces, '');
                  // check nested compound selectors s1, s2
                  expr = match[2].match(REX.SplitGroup);
                  for (i = 0, l = expr.length; l > i; ++i) {
                    expr[i] = expr[i].replace(REX.TrimSpaces, '');
                    source = compileSelector(expr[i], source, false, callback, true);
                  }
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** linguistic pseudo-classes
            // :dir( ltr / rtl ), :lang( en )
            else if ((match = selector.match(Patterns.linguistic))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'dir':
                  source = 'var p;if(' + N + '(' +
                    '(/' + match[2] + '/i.test(e.dir))||(p=s.ancestor("[dir]", e))&&' +
                    '(/' + match[2] + '/i.test(p.dir))||(e.dir==""||e.dir=="auto")&&' +
                    '(' + (match[2] == 'ltr' ? '!':'')+ RTL +'.test(e.textContent)))' +
                    '){' + source + '};';
                  break;
                case 'lang':
                  expr = '(?:^|-)' + match[2] + '(?:-|$)';
                  source = 'var p;if(' + N + '(' +
                    '(e.isConnected&&(e.lang==""&&(p=s.ancestor("[lang]",e)))&&' +
                    '(p.lang=="' + match[2] + '")||/'+ expr +'/i.test(e.lang)))' +
                    '){' + source + '};';
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** location pseudo-classes
            // :link, :visited, :target
            else if ((match = selector.match(Patterns.locationpc))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'link':
                  source = 'if(' + N + '(/^a|area|link$/i.test(e.nodeName)&&e.hasAttribute("href"))){' + source + '}';
                  break;
                case 'visited':
                  source = 'if(' + N + '(/^a|area|link$/i.test(e.nodeName)&&e.hasAttribute("href")&&e.visited)){' + source + '}';
                  break;
                case 'target':
                  source = 'if(' + N + '((s.doc.compareDocumentPosition(e)&16)&&s.doc.location.hash&&e.id==s.doc.location.hash.slice(1))){' + source + '}';
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** user actions pseudo-classes
            // :hover, :active, :focus
            else if ((match = selector.match(Patterns.useraction))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'hover':
                  source = 'hasFocus' in doc && doc.hasFocus() ?
                    'if(' + N + '(e===s.doc.hoverElement)){' + source + '}' :
                    'if(' + D + 'true){' + source + '}';
                  break;
                case 'active':
                  source = 'hasFocus' in doc && doc.hasFocus() ?
                    'if(' + N + '(e===s.doc.activeElement)){' + source + '}' :
                    'if(' + D + 'true){' + source + '}';
                  break;
                case 'focus':
                  source = 'hasFocus' in doc ?
                    'if(' + N + '(e===s.doc.activeElement&&s.doc.hasFocus()&&(e.type||e.href||typeof e.tabIndex=="number"))){' + source + '}' :
                    'if(' + N + '(e===s.doc.activeElement&&(e.type||e.href))){' + source + '}';
                  break;
                case 'focus-within':
                  source = 'hasFocus' in doc ?
                    'n=s.doc.activeElement;while(e){if(e===n||e.parentNode===n)break;}' +
                    'if(' + N + '(e===n&&s.doc.hasFocus()&&(e.type||e.href||typeof e.tabIndex=="number"))){' + source + '}' : source;
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** user interface and form pseudo-classes
            // :enabled, :disabled, :read-only, :read-write, :placeholder-shown, :default
            else if ((match = selector.match(Patterns.inputstate))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'enabled':
                  source = 'if(' + N + '(("form" in e||/^optgroup$/i.test(e.nodeName))&&"disabled" in e &&e.disabled===false' +
                    ')){' + source + '}';
                  break;
                case 'disabled':
                  // https://www.w3.org/TR/html5/forms.html#enabling-and-disabling-form-controls:-the-disabled-attribute
                  source = 'if(' + N + '(("form" in e||/^optgroup$/i.test(e.nodeName))&&"disabled" in e&&' +
                    '(e.disabled===true||(n=s.ancestor("fieldset",e))&&(n=s.first("legend",n))&&!n.contains(e))' +
                    ')){' + source + '}';
                  break;
                case 'read-only':
                  source =
                    'if(' + N + '(' +
                      '(/^textarea$/i.test(e.nodeName)&&(e.readOnly||e.disabled))||' +
                      '("|password|text|".includes("|"+e.type+"|")&&e.readOnly)' +
                    ')){' + source + '}';
                  break;
                case 'read-write':
                  source =
                    'if(' + N + '(' +
                      '((/^textarea$/i.test(e.nodeName)&&!e.readOnly&&!e.disabled)||' +
                      '("|password|text|".includes("|"+e.type+"|")&&!e.readOnly&&!e.disabled))||' +
                      '(e.hasAttribute("contenteditable")||(s.doc.designMode=="on"))' +
                    ')){' + source + '}';
                  break;
                case 'placeholder-shown':
                  source =
                    'if(' + N + '(' +
                      '(/^input|textarea$/i.test(e.nodeName))&&e.hasAttribute("placeholder")&&' +
                      '("|textarea|password|number|search|email|text|tel|url|".includes("|"+e.type+"|"))&&' +
                      '(!s.match(":focus",e))' +
                    ')){' + source + '}';
                  break;
                case 'default':
                  source =
                    'if(' + N + '("form" in e && e.form)){' +
                      'var x=0;n=[];' +
                      'if(e.type=="image")n=e.form.getElementsByTagName("input");' +
                      'if(e.type=="submit")n=e.form.elements;' +
                      'while(n[x]&&e!==n[x]){' +
                        'if(n[x].type=="image")break;' +
                        'if(n[x].type=="submit")break;' +
                        'x++;' +
                      '}' +
                    '}' +
                    'if(' + N + '(e.form&&(e===n[x]&&"|image|submit|".includes("|"+e.type+"|"))||' +
                      '((/^option$/i.test(e.nodeName))&&e.defaultSelected)||' +
                      '(("|radio|checkbox|".includes("|"+e.type+"|"))&&e.defaultChecked)' +
                    ')){' + source + '}';
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // *** input pseudo-classes (for form validation)
            // :checked, :indeterminate, :valid, :invalid, :in-range, :out-of-range, :required, :optional
            else if ((match = selector.match(Patterns.inputvalue))) {
              match[1] = match[1].toLowerCase();
              switch (match[1]) {
                case 'checked':
                  source = 'if(' + N + '(/^input$/i.test(e.nodeName)&&' +
                    '("|radio|checkbox|".includes("|"+e.type+"|")&&e.checked)||' +
                    '(/^option$/i.test(e.nodeName)&&(e.selected||e.checked))' +
                    ')){' + source + '}';
                  break;
                case 'indeterminate':
                  source =
                    'if(' + N + '(/^progress$/i.test(e.nodeName)&&!e.hasAttribute("value"))||' +
                      '(/^input$/i.test(e.nodeName)&&("checkbox"==e.type&&e.indeterminate)||' +
                      '("radio"==e.type&&e.name&&!s.first("input[name="+e.name+"]:checked",e.form))' +
                    ')){' + source + '}';
                  break;
                case 'required':
                  source =
                    'if(' + N +
                      '(/^input|select|textarea$/i.test(e.nodeName)&&e.required)' +
                    '){' + source + '}';
                  break;
                case 'optional':
                  source =
                    'if(' + N +
                      '(/^input|select|textarea$/i.test(e.nodeName)&&!e.required)' +
                    '){' + source + '}';
                  break;
                case 'invalid':
                  source =
                    'if(' + N + '((' +
                      '(/^form$/i.test(e.nodeName)&&!e.noValidate)||' +
                      '(e.willValidate&&!e.formNoValidate))&&!e.checkValidity())||' +
                      '(/^fieldset$/i.test(e.nodeName)&&s.first(":invalid",e))' +
                    '){' + source + '}';
                  break;
                case 'valid':
                  source =
                    'if(' + N + '((' +
                      '(/^form$/i.test(e.nodeName)&&!e.noValidate)||' +
                      '(e.willValidate&&!e.formNoValidate))&&e.checkValidity())||' +
                      '(/^fieldset$/i.test(e.nodeName)&&s.first(":valid",e))' +
                    '){' + source + '}';
                  break;
                case 'in-range':
                  source =
                    'if(' + N +
                      '(/^input$/i.test(e.nodeName))&&' +
                      '(e.willValidate&&!e.formNoValidate)&&' +
                      '(!e.validity.rangeUnderflow&&!e.validity.rangeOverflow)&&' +
                      '("|date|datetime-local|month|number|range|time|week|".includes("|"+e.type+"|"))&&' +
                      '("range"==e.type||e.getAttribute("min")||e.getAttribute("max"))' +
                    '){' + source + '}';
                  break;
                case 'out-of-range':
                  source =
                    'if(' + N +
                      '(/^input$/i.test(e.nodeName))&&' +
                      '(e.willValidate&&!e.formNoValidate)&&' +
                      '(e.validity.rangeUnderflow||e.validity.rangeOverflow)&&' +
                      '("|date|datetime-local|month|number|range|time|week|".includes("|"+e.type+"|"))&&' +
                      '("range"==e.type||e.getAttribute("min")||e.getAttribute("max"))' +
                    '){' + source + '}';
                  break;
                default:
                  emit('\'' + selector_string + '\'' + qsInvalid);
                  break;
              }
            }

            // allow pseudo-elements starting with single colon (:)
            // :after, :before, :first-letter, :first-line, :placeholder-shown, :-webkit-<foo-bar>
            else if ((match = selector.match(Patterns.pseudo_sng))) {
              source = 'if(' + D + '(e.nodeType==1)){' + source + '}';
            }

            // allow pseudo-elements starting with double colon (::)
            // ::after, ::before, ::marker, ::placeholder, ::inactive-selection, ::selection
            else if ((match = selector.match(Patterns.pseudo_dbl))) {
              source = 'if(' + D + '(e.nodeType==1)){' + source + '}';
            }

            else {

              // reset
              expr = false;
              status = false;

              // process registered selector extensions
              for (expr in Selectors) {
                if ((match = selector.match(Selectors[expr].Expression))) {
                  result = Selectors[expr].Callback(match, source, mode, callback);
                  if ('match' in result) { match = result.match; }
                  vars = result.modvar;
                  if (mode) {
                     // add extra select() vars
                     vars && S_VARS.indexOf(vars) < 0 && (S_VARS[S_VARS.length] = vars);
                  } else {
                     // add extra match() vars
                     vars && M_VARS.indexOf(vars) < 0 && (M_VARS[M_VARS.length] = vars);
                  }
                  // extension source code
                  source = result.source;
                  // extension status code
                  status = result.status;
                  // break on status error
                  if (status) { break; }
                }
              }

              if (!status) {
                emit('unknown pseudo-class selector \'' + selector + '\'');
                return '';
              }

              if (!expr) {
                emit('unknown token in selector \'' + selector + '\'');
                return '';
              }

            }
            break;

        default:
          emit('\'' + selector_string + '\'' + qsInvalid);
          break;

        }
        // end of switch symbol

        if (!match) {
          emit('\'' + selector_string + '\'' + qsInvalid);
          return '';
        }

        // pop last component
        selector = match.pop();
      }
      // end of while selector

      return source;
    },

  // replace ':scope' pseudo-class with element references
  makeref =
    function(selectors, element) {
      return selectors.replace(/:scope/i,
        element.nodeName.toLowerCase() +
        (element.id ? '#' + element.id : '') +
        (element.className ? '.' + element.classList[0] : ''));
    },

  // equivalent of w3c 'closest' method
  ancestor =
    function _closest(selectors, element, callback) {

      if ((/:scope/i).test(selectors)) {
        selectors = makeref(selectors, element);
      }

      while (element) {
        if (match(selectors, element, callback)) break;
        element = element.parentElement;
      }
      return element;
    },

  match_assert =
    function(f, element, callback) {
      for (var i = 0, l = f.length, r = false; l > i; ++i)
        f[i](element, callback, null, false) && (r = true);
      return r;
    },

  match_collect =
    function(selectors, callback) {
      for (var i = 0, l = selectors.length, f = [ ]; l > i; ++i)
        f[i] = compile(selectors[i], false, callback);
      return { factory: f };
    },

  // equivalent of w3c 'matches' method
  match =
    function _matches(selectors, element, callback) {

      var expressions, parsed;

      if (element && matchResolvers[selectors]) {
        return match_assert(matchResolvers[selectors].factory, element, callback);
      }

      lastMatched = selectors;

      // arguments validation
      if (arguments.length === 0) {
        emit(qsNotArgs, TypeError);
        return Config.VERBOSITY ? undefined : false;
      } else if (arguments[0] === '') {
        emit('\'\'' + qsInvalid);
        return Config.VERBOSITY ? undefined : false;
      }

      // input NULL or UNDEFINED
      if (typeof selectors != 'string') {
        selectors = '' + selectors;
      }

      if ((/:scope/i).test(selectors)) {
        selectors = makeref(selectors, element);
      }

      // normalize input string
      parsed = selectors.
        replace(/\x00|\\$/g, '\ufffd').
        replace(REX.CombineWSP, '\x20').
        replace(REX.PseudosWSP, '$1').
        replace(REX.TabCharWSP, '\t').
        replace(REX.CommaGroup, ',').
        replace(REX.TrimSpaces, '');

      // parse, validate and split possible compound selectors
      if ((expressions = parsed.match(reValidator)) && expressions.join('') == parsed) {
        expressions = parsed.match(REX.SplitGroup);
        if (parsed[parsed.length - 1] == ',') {
          emit(qsInvalid);
          return Config.VERBOSITY ? undefined : false;
        }
      } else {
        emit('\'' + selectors + '\'' + qsInvalid);
        return Config.VERBOSITY ? undefined : false;
      }

      matchResolvers[selectors] = match_collect(expressions, callback);

      return match_assert(matchResolvers[selectors].factory, element, callback);
    },

  // equivalent of w3c 'querySelector' method
  first =
    function _querySelector(selectors, context, callback) {
      if (arguments.length === 0) {
        emit(qsNotArgs, TypeError);
      }
      return select(selectors, context,
        typeof callback == 'function' ?
        function firstMatch(element) {
          callback(element);
          return false;
        } :
        function firstMatch() {
          return false;
        }
      )[0] || null;
    },

  // equivalent of w3c 'querySelectorAll' method
  select =
    function _querySelectorAll(selectors, context, callback) {

      var expressions, nodes, parsed, resolver;

      context || (context = doc);

      if (selectors) {
        if ((resolver = selectResolvers[selectors])) {
          if (resolver.context === context && resolver.callback === callback) {
            nodes = results_from(resolver, context, callback);
            Config.LIVECACHE  && !(/\[[^\]]*\]/).test(selectors) && (resolver.results = nodes);
            return typeof callback == 'function' ?
              concatCall(nodes, callback) : nodes;
          }
        }
      }

      lastSelected = selectors;

      // arguments validation
      if (arguments.length === 0) {
        emit(qsNotArgs, TypeError);
        return Config.VERBOSITY ? undefined : none;
      } else if (arguments[0] === '') {
        emit('\'\'' + qsInvalid);
        return Config.VERBOSITY ? undefined : none;
      } else if (lastContext !== context) {
        lastContext = switchContext(context);
      }

      // input NULL or UNDEFINED
      if (typeof selectors != 'string') {
        selectors = '' + selectors;
      }

      if ((/:scope/i).test(selectors)) {
        selectors = makeref(selectors, context);
      }

      // normalize input string
      parsed = selectors.
        replace(/\x00|\\$/g, '\ufffd').
        replace(REX.CombineWSP, '\x20').
        replace(REX.PseudosWSP, '$1').
        replace(REX.TabCharWSP, '\t').
        replace(REX.CommaGroup, ',').
        replace(REX.TrimSpaces, '');

      // parse, validate and split possible compound selectors
      if ((expressions = parsed.match(reValidator)) && expressions.join('') == parsed) {
        expressions = parsed.match(REX.SplitGroup);
        if (parsed[parsed.length - 1] == ',') {
          emit(qsInvalid);
          return Config.VERBOSITY ? undefined : false;
        }
      } else {
        emit('\'' + selectors + '\'' + qsInvalid);
        return Config.VERBOSITY ? undefined : false;
      }

      // save/reuse factory and closure collection
      selectResolvers[selectors] = collect(expressions, context, callback);

      nodes = results_from(selectResolvers[selectors], context, callback);

      return typeof callback == 'function' ?
        concatCall(nodes, callback) : nodes;
    },

  // optimize selectors avoiding duplicated checks
  optimize =
    function(selector, token) {
      var index = token.index,
      length = token[1].length + token[2].length;
      return selector.slice(0, index) +
        (' >+~'.indexOf(selector.charAt(index - 1)) > -1 ?
          (':['.indexOf(selector.charAt(index + length + 1)) > -1 ?
          '*' : '') : '') + selector.slice(index + length - (token[1] == '*' ? 1 : 0));
    },

  results_from =
    function(resolver, context, callback) {
      var i, k, l, list, nodes = [ ],
      f = resolver.factory, h = resolver.htmlset,
      n = resolver.nodeset, r = resolver.results;
      for (i = 0, k = 0, l = n.length; l > i; ++i) {
        list = r && h[i] ? h[i]() : compat[n[i][0]](context, n[i].slice(1))();
        if (f[i] !== null) {
          if (r && h[i]) {
            if (list.item || validate(resolver, n[i], list)) {
              ++k;
            } else {
              f[i](list, callback, context, nodes);
            }
          } else {
            f[i](list, callback, context, nodes);
          }
        } else {
          if (list.length !== 0) {
            list.length == 1 ?
              nodes[nodes.length] = list[0] :
              concatList(nodes, list);
          }
        }
        if (r && h[i]) {
          if (k == l) { nodes = r; }
        } else {
          if (l > 1 && nodes.length > 1) {
            nodes.sort(documentOrder);
            hasDupes && (nodes = unique(nodes));
          }
        }
      }
      return nodes;
    },

  // validate memoized HTMLCollection
  validate =
    function(resolver, n, s) {
      var c = 0, i = 0, l = s.length, m;
      if (l === 0) { return false; }
      m = compat[n[0]](resolver.context, n.slice(1))();
      if (m.item && s.item) {
        while (l > i) { if (m.item(i) === s.item(c)) { ++i; ++c; } else return false; }
      } else {
        while (l > i) { if (m[i] === s[c]) { ++i; ++c;} else return false; }
      }
      return m.length == c;
    },

  // prepare factory resolvers and closure collections
  collect =
    function(selectors, context, callback) {
      var i, l, token, seen = { }, factory = [ ], htmlset = [ ], nodeset = [ ];
      for (i = 0, l = selectors.length; l > i; ++i) {
        if (!seen[selectors[i]] && (seen[selectors[i]] = true)) {
          if ((token = selectors[i].match(reOptimizer)) && token[1] != ':') {
            Config.LIVECACHE && !(/\[[^\]]*\]/).test(selectors[i]) && (htmlset[i] = compat[token[1] || '*'](context, token[2]));
            nodeset[i] = (token[1] || '*') + token[2];
            selectors[i] = optimize(selectors[i], token);
          } else if (token && token[1] != ':') {
            Config.LIVECACHE && !(/\[[^\]]*\]/).test(selectors[i]) && (htmlset[i] = compat['*'](context, '*'));
            nodeset[i] = '**';
          } else {
            nodeset[i] = '**';
          }
          factory[i] = selectors[i] == '*' ? null : compile(selectors[i], true, null);
        }
      }

      return {
        callback: callback,
        context: context,
        factory: factory,
        htmlset: htmlset,
        nodeset: nodeset,
        results: null
      };
    },

  // QSA placeholders to native references
  _closest, _matches, _querySelector, _querySelectorAll,

  // overrides QSA methods (only for browsers)
  install =
    function(all) {

      // save native QSA references
      _closest = Element.prototype.closest;
      _matches = Element.prototype.matches;
      _querySelector = Document.prototype.querySelector;
      _querySelectorAll = Document.prototype.querySelectorAll;

      Element.prototype.closest =
        function closest() {
          var ctor = Object.getPrototypeOf(this).__proto__.__proto__.constructor.name;
          if (!('nodeType' in this)) { emit('\'closest\' called on an object that does not implement interface ' + ctor + '.', TypeError); }
          return arguments.length < 1 ? ancestor.apply(this, [ ]) :
                 arguments.length < 2 ? ancestor.apply(this, [ arguments[0], this ]) :
                                        ancestor.apply(this, [ arguments[0], this, typeof arguments[1] == 'function' ? arguments[1] : undefined ]);
        };

      Element.prototype.matches =
        function matches() {
          var ctor = Object.getPrototypeOf(this).__proto__.__proto__.constructor.name;
          if (!('nodeType' in this)) { emit('\'matches\' called on an object that does not implement interface ' + ctor + '.', TypeError); }
          return arguments.length < 1 ? match.apply(this, [ ]) :
                 arguments.length < 2 ? match.apply(this, [ arguments[0], this ]) :
                                        match.apply(this, [ arguments[0], this, typeof arguments[1] == 'function' ? arguments[1] : undefined ]);
        };

      Element.prototype.querySelector =
      Document.prototype.querySelector =
      DocumentFragment.prototype.querySelector =
        function querySelector() {
          var ctor = Object.getPrototypeOf(this).__proto__.__proto__.constructor.name;
          if (!('nodeType' in this)) { emit('\'querySelector\' called on an object that does not implement interface ' + ctor + '.', TypeError); }
          return arguments.length < 1 ? first.apply(this, [ ]) :
                 arguments.length < 2 ? first.apply(this, [ arguments[0], this ]) :
                                        first.apply(this, [ arguments[0], this, typeof arguments[1] == 'function' ? arguments[1] : undefined ]);
        };

      Element.prototype.querySelectorAll =
      Document.prototype.querySelectorAll =
      DocumentFragment.prototype.querySelectorAll =
        function querySelectorAll() {
          var ctor = Object.getPrototypeOf(this).__proto__.__proto__.constructor.name;
          if (!('nodeType' in this)) { emit('\'querySelectorAll\' called on an object that does not implement interface ' + ctor + '.', TypeError); }
          return arguments.length < 1 ? select.apply(this, [ ]) :
                 arguments.length < 2 ? select.apply(this, [ arguments[0], this ]) :
                                        select.apply(this, [ arguments[0], this, typeof arguments[1] == 'function' ? arguments[1] : undefined ]);
        };

      if (all) {
        document.addEventListener('load', function(e) {
          var c, d, r, s, t = e.target;
          if (/iframe/i.test(t.nodeName)) {
            c = '(' + Export + ')(this, ' + Factory + ');'; d = t.contentDocument;
            s = d.createElement('script'); s.textContent = c + 'NW.Dom.install()';
            r = d.documentElement; r.removeChild(r.insertBefore(s, r.firstChild));
          }
        }, true);
      }

    },

  // restore QSA methods (only for browsers)
  uninstall =
    function() {
      // reinstates QSA native references
      Element.prototype.closest = _closest;
      Element.prototype.matches = _matches;
      Element.prototype.querySelector =
      Document.prototype.querySelector =
      DocumentFragment.prototype.querySelector = _querySelector;
      Element.prototype.querySelectorAll =
      Document.prototype.querySelectorAll =
      DocumentFragment.prototype.querySelectorAll = _querySelectorAll;
    },

  // empty set
  none = Array(),

  // context
  lastContext,

  // selector
  lastMatched,
  lastSelected,

  // cached lambdas
  matchLambdas = { },
  selectLambdas = { },

  // cached resolvers
  matchResolvers = { },
  selectResolvers = { },

  // passed to resolvers
  Snapshot = {

    doc: doc,
    from: doc,
    root: root,

    byTag: byTag,

    first: first,
    match: match,

    ancestor: ancestor,

    nthOfType: nthOfType,
    nthElement: nthElement,

    hasAttributeNS: hasAttributeNS
  },

  // public exported methods/objects
  Dom = {

    // exported cache objects

    lastMatched: lastMatched,
    lastSelected: lastSelected,

    matchLambdas: matchLambdas,
    selectLambdas: selectLambdas,

    matchResolvers: matchResolvers,
    selectResolvers: selectResolvers,

    // exported compiler macros

    CFG: CFG,

    M_BODY: M_BODY,
    S_BODY: S_BODY,
    M_TEST: M_TEST,
    S_TEST: S_TEST,

    // exported engine methods

    byId: byId,
    byTag: byTag,
    byClass: byClass,

    match: match,
    first: first,
    select: select,
    closest: ancestor,

    compile: compile,
    configure: configure,

    emit: emit,
    Config: Config,
    Snapshot: Snapshot,

    Version: version,

    install: install,
    uninstall: uninstall,

    Operators: Operators,
    Selectors: Selectors,

    // register a new selector combinator symbol and its related function resolver
    registerCombinator:
      function(combinator, resolver) {
        var i = 0, l = combinator.length, symbol;
        for (; l > i; ++i) {
          if (combinator[i] != '=') {
            symbol = combinator[i];
            break;
          }
        }
        if (CFG.combinators.indexOf(symbol) < 0) {
          CFG.combinators = CFG.combinators.replace('](', symbol + '](');
          CFG.combinators = CFG.combinators.replace('])', symbol + '])');
          Combinators[combinator] = resolver;
          setIdentifierSyntax();
        } else {
          console.warn('Warning: the \'' + combinator + '\' combinator is already registered.');
        }
      },

    // register a new attribute operator symbol and its related function resolver
    registerOperator:
      function(operator, resolver) {
        var i = 0, l = operator.length, symbol;
        for (; l > i; ++i) {
          if (operator[i] != '=') {
            symbol = operator[i];
            break;
          }
        }
        if (CFG.operators.indexOf(symbol) < 0 && !Operators[operator]) {
          CFG.operators = CFG.operators.replace(']=', symbol + ']=');
          Operators[operator] = resolver;
          setIdentifierSyntax();
        } else {
          console.warn('Warning: the \'' + operator + '\' operator is already registered.');
        }
      },

    // register a new selector symbol and its related function resolver
    registerSelector:
      function(name, rexp, func) {
        Selectors[name] || (Selectors[name] = {
          Expression: rexp,
          Callback: func
        });
      }

  };

  initialize(doc);

  return Dom;

});
