/*
 * Copyright (C) 2007-2017 Diego Perini
 * All rights reserved.
 *
 * nwmatcher.js - A fast CSS selector engine and matcher
 *
 * Author: Diego Perini <diego.perini at gmail com>
 * Version: 1.4.3
 * Created: 20070722
 * Release: 20171011
 *
 * License:
 *  http://javascript.nwbox.com/NWMatcher/MIT-LICENSE
 * Download:
 *  http://javascript.nwbox.com/NWMatcher/nwmatcher.js
 */

(function(global, factory) {

  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);
  }

})(this, function(global) {

  var version = 'nwmatcher-1.4.3',

  // processing context & root element
  doc = global.document,
  root = doc.documentElement,

  // save utility methods references
  slice = [ ].slice,

  // persist previous parsed data
  isSingleMatch,
  isSingleSelect,

  lastSlice,
  lastContext,
  lastPosition,

  lastMatcher,
  lastSelector,

  lastPartsMatch,
  lastPartsSelect,

  // accepted prefix identifiers
  // (id, class & pseudo-class)
  prefixes = '(?:[#.:]|::)?',

  // accepted attribute operators
  operators = '([~*^$|!]?={1})',

  // accepted whitespace characters
  whitespace = '[\\x20\\t\\n\\r\\f]',

  // 4 combinators F E, F>E, F+E, F~E
  combinators = '\\x20|[>+~](?=[^>+~])',

  // an+b format params for pseudo-classes
  pseudoparms = '(?:[-+]?\\d*n)?[-+]?\\d*',

  // skip [ ], ( ), { } brackets groups
  skip_groups = '\\[.*\\]|\\(.*\\)|\\{.*\\}',

  // any escaped char
  any_esc_chr = '\\\\.',
  // alpha chars & low dash
  alphalodash = '[_a-zA-Z]',
  // non-ascii chars (utf-8)
  non_asc_chr = '[^\\x00-\\x9f]',
  // escape sequences in strings
  escaped_chr = '\\\\[^\\n\\r\\f0-9a-fA-F]',
  // Unicode chars including trailing whitespace
  unicode_chr = '\\\\[0-9a-fA-F]{1,6}(?:\\r\\n|' + whitespace + ')?',

  // CSS quoted string values
  quotedvalue = '"[^"\\\\]*(?:\\\\.[^"\\\\]*)*"' + "|'[^'\\\\]*(?:\\\\.[^'\\\\]*)*'",

  // regular expression used to skip single/nested brackets groups (round, square, curly)
  // used to split comma groups excluding commas inside quotes '' "" or brackets () [] {}
  reSplitGroup = /([^,\\()[\]]+|\[[^[\]]*\]|\[.*\]|\([^()]+\)|\(.*\)|\{[^{}]+\}|\{.*\}|\\.)+/g,

  // regular expression to trim extra leading/trailing whitespace in selector strings
  // whitespace is any combination of these 5 character [\x20\t\n\r\f]
  // http://www.w3.org/TR/css3-selectors/#selector-syntax
  reTrimSpaces = RegExp('[\\n\\r\\f]|^' + whitespace + '+|' + whitespace + '+$', 'g'),

  // regular expression used in convertEscapes and unescapeIdentifier
  reEscapedChars = /\\([0-9a-fA-F]{1,6}[\x20\t\n\r\f]?|.)|([\x22\x27])/g,

  // for in excess whitespace removal
  reWhiteSpace = /[\x20\t\n\r\f]+/g,

  standardValidator, extendedValidator, reValidator,

  attrcheck, attributes, attrmatcher, pseudoclass,

  reOptimizeSelector, reSimpleNot, reSplitToken,

  Optimize, reClass, reSimpleSelector,

  // http://www.w3.org/TR/css3-syntax/#characters
  // unicode/ISO 10646 characters \xA0 and higher
  // NOTE: Safari 2.0.x crashes with escaped (\\)
  // Unicode ranges in regular expressions so we
  // use a negated character range class instead
  // now assigned at runtime from config options
  identifier,

  // placeholder for extensions
  extensions = '.+',

  // precompiled Regular Expressions
  Patterns = {
    // structural pseudo-classes and child selectors
    spseudos: /^\:(root|empty|(?:first|last|only)(?:-child|-of-type)|nth(?:-last)?(?:-child|-of-type)\(\s*(even|odd|(?:[-+]{0,1}\d*n\s*)?[-+]{0,1}\s*\d*)\s*\))?(.*)/i,
    // uistates + dynamic + negation pseudo-classes
    dpseudos: /^\:(link|visited|target|active|focus|hover|checked|disabled|enabled|selected|lang\(([-\w]{2,})\)|(?:matches|not)\(\s*(:nth(?:-last)?(?:-child|-of-type)\(\s*(?:even|odd|(?:[-+]{0,1}\d*n\s*)?[-+]{0,1}\s*\d*)\s*\)|[^()]*)\s*\))?(.*)/i,
    // pseudo-elements selectors
    epseudos: /^((?:[:]{1,2}(?:after|before|first-letter|first-line))|(?:[:]{2,2}(?:selection|backdrop|placeholder)))?(.*)/i,
    // E > F
    children: RegExp('^' + whitespace + '*\\>' + whitespace + '*(.*)'),
    // E + F
    adjacent: RegExp('^' + whitespace + '*\\+' + whitespace + '*(.*)'),
    // E ~ F
    relative: RegExp('^' + whitespace + '*\\~' + whitespace + '*(.*)'),
    // E F
    ancestor: RegExp('^' + whitespace + '+(.*)'),
    // all
    universal: RegExp('^\\*(.*)')
  },

  Tokens = {
    prefixes: prefixes,
    identifier: identifier,
    attributes: attributes
  },

  /*----------------------------- FEATURE TESTING ----------------------------*/

  // detect native methods
  isNative = (function() {
    var re = / \w+\(/,
    isnative = String(({ }).toString).replace(re, ' (');
    return function(method) {
      return method && typeof method != 'string' &&
        isnative == String(method).replace(re, ' (');
    };
  })(),

  // NATIVE_XXXXX true if method exist and is callable
  // detect if DOM methods are native in browsers
  NATIVE_FOCUS = isNative(doc.hasFocus),
  NATIVE_QSAPI = isNative(doc.querySelector),
  NATIVE_GEBID = isNative(doc.getElementById),
  NATIVE_GEBTN = isNative(root.getElementsByTagName),
  NATIVE_GEBCN = isNative(root.getElementsByClassName),

  // detect native getAttribute/hasAttribute methods,
  // frameworks extend these to elements, but it seems
  // this does not work for XML namespaced attributes,
  // used to check both getAttribute/hasAttribute in IE
  NATIVE_GET_ATTRIBUTE = isNative(root.getAttribute),
  NATIVE_HAS_ATTRIBUTE = isNative(root.hasAttribute),

  // check if slice() can convert nodelist to array
  // see http://yura.thinkweb2.com/cft/
  NATIVE_SLICE_PROTO =
    (function() {
      var isBuggy = false;
      try {
        isBuggy = !!slice.call(doc.childNodes, 0)[0];
      } catch(e) { }
      return isBuggy;
    })(),

  // supports the new traversal API
  NATIVE_TRAVERSAL_API =
    'nextElementSibling' in root && 'previousElementSibling' in root,

  // BUGGY_XXXXX true if method is feature tested and has known bugs
  // detect buggy gEBID
  BUGGY_GEBID = NATIVE_GEBID ?
    (function() {
      var isBuggy = true, x = 'x' + String(+new Date),
        a = doc.createElementNS ? 'a' : '<a name="' + x + '">';
      (a = doc.createElement(a)).name = x;
      root.insertBefore(a, root.firstChild);
      isBuggy = !!doc.getElementById(x);
      root.removeChild(a);
      return isBuggy;
    })() :
    true,

  // detect IE gEBTN comment nodes bug
  BUGGY_GEBTN = NATIVE_GEBTN ?
    (function() {
      var div = doc.createElement('div');
      div.appendChild(doc.createComment(''));
      return !!div.getElementsByTagName('*')[0];
    })() :
    true,

  // detect Opera gEBCN second class and/or UTF8 bugs as well as Safari 3.2
  // caching class name results and not detecting when changed,
  // tests are based on the jQuery selector test suite
  BUGGY_GEBCN = NATIVE_GEBCN ?
    (function() {
      var isBuggy, div = doc.createElement('div'), test = '\u53f0\u5317';

      // Opera tests
      div.appendChild(doc.createElement('span')).
        setAttribute('class', test + 'abc ' + test);
      div.appendChild(doc.createElement('span')).
        setAttribute('class', 'x');

      isBuggy = !div.getElementsByClassName(test)[0];

      // Safari test
      div.lastChild.className = test;
      return isBuggy || div.getElementsByClassName(test).length != 2;
    })() :
    true,

  // detect IE bug with dynamic attributes
  BUGGY_GET_ATTRIBUTE = NATIVE_GET_ATTRIBUTE ?
    (function() {
      var input = doc.createElement('input');
      input.setAttribute('value', 5);
      return input.defaultValue != 5;
    })() :
    true,

  // detect IE bug with non-standard boolean attributes
  BUGGY_HAS_ATTRIBUTE = NATIVE_HAS_ATTRIBUTE ?
    (function() {
      var option = doc.createElement('option');
      option.setAttribute('selected', 'selected');
      return !option.hasAttribute('selected');
    })() :
    true,

  // detect Safari bug with selected option elements
  BUGGY_SELECTED =
    (function() {
      var select = doc.createElement('select');
      select.appendChild(doc.createElement('option'));
      return !select.firstChild.selected;
    })(),

  // initialized with the loading context
  // and reset for each different context
  BUGGY_QUIRKS_GEBCN,
  BUGGY_QUIRKS_QSAPI,

  QUIRKS_MODE,
  XML_DOCUMENT,

  // detect Opera browser
  OPERA = typeof global.opera != 'undefined' &&
    (/opera/i).test(({ }).toString.call(global.opera)),

  // skip simple selector optimizations for Opera >= 11
  OPERA_QSAPI = OPERA && parseFloat(global.opera.version()) >= 11,

  // check Selector API implementations
  RE_BUGGY_QSAPI = NATIVE_QSAPI ?
    (function() {
      var pattern = [ ], context, element,

      expect = function(selector, element, n) {
        var result = false;
        context.appendChild(element);
        try { result = context.querySelectorAll(selector).length == n; } catch(e) { }
        while (context.firstChild) { context.removeChild(context.firstChild); }
        return result;
      };

      // certain bugs can only be detected in standard documents
      // to avoid writing a live loading document create a fake one
      if (doc.implementation && doc.implementation.createDocument) {
        // use a shadow document body as context
        context = doc.implementation.createDocument('', '', null).
          appendChild(doc.createElement('html')).
          appendChild(doc.createElement('head')).parentNode.
          appendChild(doc.createElement('body'));
      } else {
        // use an unattached div node as context
        context = doc.createElement('div');
      }

      // fix for Safari 8.x and other engines that
      // fail querying filtered sibling combinators
      element = doc.createElement('div');
      element.innerHTML = '<p id="a"></p><br>';
      expect('p#a+*', element, 0) &&
        pattern.push('\\w+#\\w+.*[+~]');

      // ^= $= *= operators bugs with empty values (Opera 10 / IE8)
      element = doc.createElement('p');
      element.setAttribute('class', '');
      expect('[class^=""]', element, 1) &&
        pattern.push('[*^$]=[\\x20\\t\\n\\r\\f]*(?:""|' + "'')");

      // :checked bug with option elements (Firefox 3.6.x)
      // it wrongly includes 'selected' options elements
      // HTML5 rules says selected options also match
      element = doc.createElement('option');
      element.setAttribute('selected', 'selected');
      expect(':checked', element, 0) &&
        pattern.push(':checked');

      // :enabled :disabled bugs with hidden fields (Firefox 3.5)
      // http://www.w3.org/TR/html5/links.html#selector-enabled
      // http://www.w3.org/TR/css3-selectors/#enableddisabled
      // not supported by IE8 Query Selector
      element = doc.createElement('input');
      element.setAttribute('type', 'hidden');
      expect(':enabled', element, 0) &&
        pattern.push(':enabled', ':disabled');

      // :link bugs with hyperlinks matching (Firefox/Safari)
      element = doc.createElement('link');
      element.setAttribute('href', 'x');
      expect(':link', element, 1) ||
        pattern.push(':link');

      // avoid attribute selectors for IE QSA
      if (BUGGY_HAS_ATTRIBUTE) {
        // IE fails in reading:
        // - original values for input/textarea
        // - original boolean values for controls
        pattern.push('\\[[\\x20\\t\\n\\r\\f]*(?:checked|disabled|ismap|multiple|readonly|selected|value)');
      }

      return pattern.length ?
        RegExp(pattern.join('|')) :
        { 'test': function() { return false; } };

    })() :
    true,

  /*----------------------------- LOOKUP OBJECTS -----------------------------*/

  IE_LT_9 = typeof doc.addEventListener != 'function',

  LINK_NODES = { 'a': 1, 'A': 1, 'area': 1, 'AREA': 1, 'link': 1, 'LINK': 1 },

  // boolean attributes should return attribute name instead of true/false
  ATTR_BOOLEAN = {
    'checked': 1, 'disabled': 1, 'ismap': 1,
    'multiple': 1, 'readonly': 1, 'selected': 1
  },

  // dynamic attributes that needs to be checked against original HTML value
  ATTR_DEFAULT = {
    'value': 'defaultValue',
    'checked': 'defaultChecked',
    'selected': 'defaultSelected'
  },

  // attributes referencing URI data values need special treatment in IE
  ATTR_URIDATA = {
    'action': 2, 'cite': 2, 'codebase': 2, 'data': 2, 'href': 2,
    'longdesc': 2, 'lowsrc': 2, 'src': 2, 'usemap': 2
  },

  // HTML 5 draft specifications
  // http://www.whatwg.org/specs/web-apps/current-work/#selectors
  HTML_TABLE = {
    // NOTE: class name attribute selectors must always be treated using a
    // case-sensitive match, this has changed from previous specifications
    '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
  },

  /*-------------------------- REGULAR EXPRESSIONS ---------------------------*/

  // placeholder to add functionalities
  Selectors = {
    // as a simple example this will check
    // for chars not in standard ascii table
    //
    // 'mySpecialSelector': {
    //  'Expression': /\u0080-\uffff/,
    //  'Callback': mySelectorCallback
    // }
    //
    // 'mySelectorCallback' will be invoked
    // only after passing all other standard
    // checks and only if none of them worked
  },

  // attribute operators
  Operators = {
     '=': "n=='%m'",
    '^=': "n.indexOf('%m')==0",
    '*=': "n.indexOf('%m')>-1",
    '|=': "(n+'-').indexOf('%m-')==0",
    '~=': "(' '+n+' ').indexOf(' %m ')>-1",
    '$=': "n.substr(n.length-'%m'.length)=='%m'"
  },

  /*------------------------------ UTIL METHODS ------------------------------*/

  // concat elements to data
  concatList =
    function(data, elements) {
      var i = -1, element;
      if (!data.length && Array.slice)
        return Array.slice(elements);
      while ((element = elements[++i]))
        data[data.length] = element;
      return data;
    },

  // concat elements to data and callback
  concatCall =
    function(data, elements, callback) {
      var i = -1, element;
      while ((element = elements[++i])) {
        if (false === callback(data[data.length] = element)) { break; }
      }
      return data;
    },

  // change context specific variables
  switchContext =
    function(from, force) {
      var div, oldDoc = doc;
      // save passed context
      lastContext = from;
      // set new context document
      doc = from.ownerDocument || from;
      if (force || oldDoc !== doc) {
        // set document root
        root = doc.documentElement;
        // set host environment flags
        XML_DOCUMENT = doc.createElement('DiV').nodeName == 'DiV';

        // In quirks mode css class names are case insensitive.
        // In standards mode they are case sensitive. See docs:
        // https://developer.mozilla.org/en/Mozilla_Quirks_Mode_Behavior
        // http://www.whatwg.org/specs/web-apps/current-work/#selectors
        QUIRKS_MODE = !XML_DOCUMENT &&
          typeof doc.compatMode == 'string' ?
          doc.compatMode.indexOf('CSS') < 0 :
          (function() {
            var style = doc.createElement('div').style;
            return style && (style.width = 1) && style.width == '1px';
          })();

        div = doc.createElement('div');
        div.appendChild(doc.createElement('p')).setAttribute('class', 'xXx');
        div.appendChild(doc.createElement('p')).setAttribute('class', 'xxx');

        // GEBCN buggy in quirks mode, match count is:
        // Firefox 3.0+ [xxx = 1, xXx = 1]
        // Opera 10.63+ [xxx = 0, xXx = 2]
        BUGGY_QUIRKS_GEBCN =
          !XML_DOCUMENT && NATIVE_GEBCN && QUIRKS_MODE &&
          (div.getElementsByClassName('xxx').length != 2 ||
          div.getElementsByClassName('xXx').length != 2);

        // QSAPI buggy in quirks mode, match count is:
        // At least Chrome 4+, Firefox 3.5+, Opera 10.x+, Safari 4+ [xxx = 1, xXx = 2]
        // Safari 3.2 QSA doesn't work with mixedcase in quirksmode [xxx = 1, xXx = 0]
        // https://bugs.webkit.org/show_bug.cgi?id=19047
        // must test the attribute selector '[class~=xxx]'
        // before '.xXx' or the bug may not present itself
        BUGGY_QUIRKS_QSAPI =
          !XML_DOCUMENT && NATIVE_QSAPI && QUIRKS_MODE &&
          (div.querySelectorAll('[class~=xxx]').length != 2 ||
          div.querySelectorAll('.xXx').length != 2);

        Config.CACHING && Dom.setCache(true, doc);
      }
    },

  // 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 str.replace(reEscapedChars,
          function(substring, p1, p2) {
            // unescaped " or '
            return p2 ? '\\' + p2 :
              // javascript strings are UTF-16 encoded
              /^[0-9a-fA-F]/.test(p1) ? codePointToUTF16(parseInt(p1, 16)) :
              // \' \"
              /^[\\\x22\x27]/.test(p1) ? substring :
              // \g \h \. \# etc
              p1;
          }
        );
    },

  // convert escape sequence in a CSS string or identifier
  // to javascript string with characters representations
  unescapeIdentifier =
    function(str) {
      return str.replace(reEscapedChars,
          function(substring, p1, p2) {
            // unescaped " or '
            return p2 ? p2 :
              // javascript strings are UTF-16 encoded
              /^[0-9a-fA-F]/.test(p1) ? stringFromCodePoint(parseInt(p1, 16)) :
              // \' \"
              /^[\\\x22\x27]/.test(p1) ? substring :
              // \g \h \. \# etc
              p1;
          }
        );
    },

  /*------------------------------ DOM METHODS -------------------------------*/

  // element by id (raw)
  // @return reference or null
  byIdRaw =
    function(id, elements) {
      var i = -1, element;
      while ((element = elements[++i])) {
        if (element.getAttribute('id') == id) {
          break;
        }
      }
      return element || null;
    },

  // element by id
  // @return reference or null
  _byId = !BUGGY_GEBID ?
    function(id, from) {
      id = (/\\/).test(id) ? unescapeIdentifier(id) : id;
      return from.getElementById && from.getElementById(id) ||
        byIdRaw(id, from.getElementsByTagName('*'));
    } :
    function(id, from) {
      var element = null;
      id = (/\\/).test(id) ? unescapeIdentifier(id) : id;
      if (XML_DOCUMENT || from.nodeType != 9) {
        return byIdRaw(id, from.getElementsByTagName('*'));
      }
      if ((element = from.getElementById(id)) &&
        element.name == id && from.getElementsByName) {
        return byIdRaw(id, from.getElementsByName(id));
      }
      return element;
    },

  // publicly exposed byId
  // @return reference or null
  byId =
    function(id, from) {
      from || (from = doc);
      if (lastContext !== from) { switchContext(from); }
      return _byId(id, from);
    },

  // elements by tag (raw)
  // @return array
  byTagRaw =
    function(tag, from) {
      var any = tag == '*', element = from, elements = [ ], next = element.firstChild;
      any || (tag = tag.toUpperCase());
      while ((element = next)) {
        if (element.tagName > '@' && (any || element.tagName.toUpperCase() == tag)) {
          elements[elements.length] = element;
        }
        if ((next = element.firstChild || element.nextSibling)) continue;
        while (!next && (element = element.parentNode) && element !== from) {
          next = element.nextSibling;
        }
      }
      return elements;
    },

  // elements by tag
  // @return array
  _byTag = !BUGGY_GEBTN && NATIVE_SLICE_PROTO ?
    function(tag, from) {
      return XML_DOCUMENT || from.nodeType == 11 ? byTagRaw(tag, from) :
        slice.call(from.getElementsByTagName(tag), 0);
    } :
    function(tag, from) {
      var i = -1, j = i, data = [ ], element,
        elements = XML_DOCUMENT || from.nodeType == 11 ?
        byTagRaw(tag, from) : from.getElementsByTagName(tag);
      if (tag == '*') {
        while ((element = elements[++i])) {
          if (element.nodeName > '@') {
            data[++j] = element;
          }
        }
      } else {
        while ((element = elements[++i])) {
          data[i] = element;
        }
      }
      return data;
    },

  // publicly exposed byTag
  // @return array
  byTag =
    function(tag, from) {
      from || (from = doc);
      if (lastContext !== from) { switchContext(from); }
      return _byTag(tag, from);
    },

  // publicly exposed byName
  // @return array
  byName =
    function(name, from) {
      return select('[name="' + name.replace(/\\([^\\]{1})/g, '$1') + '"]', from);
    },

  // elements by class (raw)
  // @return array
  byClassRaw =
    function(name, from) {
      var i = -1, j = i, data = [ ], element, elements = _byTag('*', from), n;
      name = ' ' + (QUIRKS_MODE ? name.toLowerCase() : name) + ' ';
      while ((element = elements[++i])) {
        n = XML_DOCUMENT ? element.getAttribute('class') : element.className;
        if (n && n.length && (' ' + (QUIRKS_MODE ? n.toLowerCase() : n).
          replace(reWhiteSpace, ' ') + ' ').indexOf(name) > -1) {
          data[++j] = element;
        }
      }
      return data;
    },

  // elements by class
  // @return array
  _byClass =
    function(name, from) {
      name = QUIRKS_MODE ? name.toLowerCase() : name;
      name = (/\\/).test(name) ? unescapeIdentifier(name) : name;
      return (BUGGY_GEBCN || BUGGY_QUIRKS_GEBCN || XML_DOCUMENT || !from.getElementsByClassName) ?
        byClassRaw(name, from) : slice.call(from.getElementsByClassName(name));
    },

  // publicly exposed byClass
  // @return array
  byClass =
    function(name, from) {
      from || (from = doc);
      if (lastContext !== from) { switchContext(from); }
      return _byClass(name, from);
    },

  // check element is descendant of container
  // @return boolean
  contains = 'compareDocumentPosition' in root ?
    function(container, element) {
      return (container.compareDocumentPosition(element) & 16) == 16;
    } : 'contains' in root ?
    function(container, element) {
      return container !== element && container.contains(element);
    } :
    function(container, element) {
      while ((element = element.parentNode)) {
        if (element === container) return true;
      }
      return false;
    },

  // attribute value
  // @return string
  getAttribute = !BUGGY_GET_ATTRIBUTE && !IE_LT_9 ?
    function(node, attribute) {
      return node.getAttribute(attribute);
    } :
    function(node, attribute) {
      attribute = attribute.toLowerCase();
      if (typeof node[attribute] == 'object') {
        return node.attributes[attribute] &&
          node.attributes[attribute].value;
      }
      return (
        // 'type' can only be read by using native getAttribute
        attribute == 'type' ? node.getAttribute(attribute) :
        // specific URI data attributes (parameter 2 to fix IE bug)
        ATTR_URIDATA[attribute] ? node.getAttribute(attribute, 2) :
        // boolean attributes should return name instead of true/false
        ATTR_BOOLEAN[attribute] ? node.getAttribute(attribute) ? attribute : 'false' :
          (node = node.getAttributeNode(attribute)) && node.value);
    },

  // attribute presence
  // @return boolean
  hasAttribute = !BUGGY_HAS_ATTRIBUTE && !IE_LT_9 ?
    function(node, attribute) {
      return XML_DOCUMENT ?
        !!node.getAttribute(attribute) :
        node.hasAttribute(attribute);
    } :
    function(node, attribute) {
      // read the node attribute object
      var obj = node.getAttributeNode(attribute = attribute.toLowerCase());
      return ATTR_DEFAULT[attribute] && attribute != 'value' ?
        node[ATTR_DEFAULT[attribute]] : obj && obj.specified;
    },

  // check node emptyness
  // @return boolean
  isEmpty =
    function(node) {
      node = node.firstChild;
      while (node) {
        if (node.nodeType == 3 || node.nodeName > '@') return false;
        node = node.nextSibling;
      }
      return true;
    },

  // check if element matches the :link pseudo
  // @return boolean
  isLink =
    function(element) {
      return hasAttribute(element,'href') && LINK_NODES[element.nodeName];
    },

  // child position by nodeType
  // @return number
  nthElement =
    function(element, last) {
      var count = 1, succ = last ? 'nextSibling' : 'previousSibling';
      while ((element = element[succ])) {
        if (element.nodeName > '@') ++count;
      }
      return count;
    },

  // child position by nodeName
  // @return number
  nthOfType =
    function(element, last) {
      var count = 1, succ = last ? 'nextSibling' : 'previousSibling', type = element.nodeName;
      while ((element = element[succ])) {
        if (element.nodeName == type) ++count;
      }
      return count;
    },

  /*------------------------------- DEBUGGING --------------------------------*/

  // get/set (string/object) working modes
  configure =
    function(option) {
      if (typeof option == 'string') { return !!Config[option]; }
      if (typeof option != 'object') { return Config; }
      for (var i in option) {
        Config[i] = !!option[i];
        if (i == 'SIMPLENOT') {
          matchContexts = { };
          matchResolvers = { };
          selectContexts = { };
          selectResolvers = { };
          if (!Config[i]) { Config['USE_QSAPI'] = false; }
        } else if (i == 'USE_QSAPI') {
          Config[i] = !!option[i] && NATIVE_QSAPI;
        }
      }
      setIdentifierSyntax();
      reValidator = RegExp(Config.SIMPLENOT ?
        standardValidator : extendedValidator);
      return true;
    },

  // control user notifications
  emit =
    function(message) {
      if (Config.VERBOSITY) { throw Error(message); }
      if (Config.LOGERRORS && console && console.log) {
        console.log(message);
      }
    },

  Config = {

    // true to enable caching of result sets, false to disable
    CACHING: false,

    // true to allow CSS escaped identifiers, false to disallow
    ESCAPECHR: true,

    // true to allow identifiers containing non-ASCII (utf-8) chars
    NON_ASCII: true,

    // switch syntax RE, true to use Level 3, false to use Level 2
    SELECTOR3: true,

    // true to allow identifiers containing Unicode (utf-16) chars
    UNICODE16: true,

    // by default do not add missing left/right context
    // to mangled selector strings like "+div" or "ul>"
    // callable Dom.shortcuts method has to be available
    SHORTCUTS: false,

    // true to disable complex selectors nested in
    // ':not()' pseudo-classes as for specifications
    SIMPLENOT: true,

    // true to match lowercase tag names of SVG elements in HTML
    SVG_LCASE: false,

    // strict QSA match all non-unique IDs (false)
    // speed & libs compat match unique ID (true)
    UNIQUE_ID: true,

    // true to follow HTML5 specs handling of ":checked"
    // pseudo-class and similar UI states (indeterminate)
    USE_HTML5: true,

    // true to use browsers native Query Selector API if available
    USE_QSAPI: NATIVE_QSAPI,

    // true to throw exceptions, false to skip throwing exceptions
    VERBOSITY: true,

    // true to print console errors or warnings, false to mute them
    LOGERRORS: true

  },

  /*---------------------------- COMPILER METHODS ----------------------------*/

  // init REs and context
  initialize =
    function(doc) {
      setIdentifierSyntax();
      switchContext(doc, true);
    },

  // set/reset default identifier syntax
  // based on user configuration options
  // rebuild the validator and other REs
  setIdentifierSyntax =
    function() {

      var syntax = '', start = Config['SELECTOR3'] ? '-{2}|' : '';

      Config['NON_ASCII'] && (syntax += '|' + non_asc_chr);
      Config['UNICODE16'] && (syntax += '|' + unicode_chr);
      Config['ESCAPECHR'] && (syntax += '|' + escaped_chr);

      syntax += (Config['UNICODE16'] || Config['ESCAPECHR']) ? '' : '|' + any_esc_chr;

      identifier = '-?(?:' + start + alphalodash + syntax + ')(?:-|[0-9]|' + alphalodash + syntax + ')*';

      // build attribute string
      attrcheck = '(' + quotedvalue + '|' + identifier + ')';
      attributes = whitespace + '*(' + identifier + '(?::' + identifier + ')?)' +
        whitespace + '*(?:' + operators + whitespace + '*' + attrcheck + ')?' + whitespace + '*' + '(i)?' + whitespace + '*';
      attrmatcher = attributes.replace(attrcheck, '([\\x22\\x27]*)((?:\\\\?.)*?)\\3');

      // build pseudoclass string
      pseudoclass = '((?:' +
        // an+b parameters or quoted string
        pseudoparms + '|' + quotedvalue + '|' +
        // id, class, pseudo-class selector
        prefixes + identifier + '|' +
        // nested HTML attribute selector
        '\\[' + attributes + '\\]|' +
        // nested pseudo-class selector
        '\\(.+\\)|' + whitespace + '*|' +
        // nested pseudos/separators
        ',)+)';

      // CSS3: syntax scanner and
      // one pass validation only
      // using regular expression
      standardValidator =
        // discard start
        '(?=[\\x20\\t\\n\\r\\f]*[^>+~(){}<>])' +
        // open match group
        '(' +
        //universal selector
        '\\*' +
        // id/class/tag/pseudo-class identifier
        '|(?:' + prefixes + identifier + ')' +
        // combinator selector
        '|' + combinators +
        // HTML attribute selector
        '|\\[' + attributes + '\\]' +
        // pseudo-classes parameters
        '|\\(' + pseudoclass + '\\)' +
        // dom properties selector (extension)
        '|\\{' + extensions + '\\}' +
        // selector group separator (comma)
        '|(?:,|' + whitespace + '*)' +
        // close match group
        ')+';

      // only allow simple selectors nested in ':not()' pseudo-classes
      reSimpleNot = RegExp('^(' +
        '(?!:not)' +
        '(' + prefixes + identifier +
        '|\\([^()]*\\))+' +
        '|\\[' + attributes + '\\]' +
        ')$');

      // split last, right most, selector group token
      reSplitToken = RegExp('(' +
        prefixes + identifier + '|' +
        '\\[' + attributes + '\\]|' +
        '\\(' + pseudoclass + '\\)|' +
        '\\\\.|[^\\x20\\t\\n\\r\\f>+~])+', 'g');

      reOptimizeSelector = RegExp(identifier + '|^$');

      reSimpleSelector = RegExp(
        BUGGY_GEBTN && BUGGY_GEBCN || OPERA ?
          '^#?' + identifier + '$' : BUGGY_GEBTN ?
          '^[.#]?' + identifier + '$' : BUGGY_GEBCN ?
          '^(?:\\*|#' + identifier + ')$' :
          '^(?:\\*|[.#]?' + identifier + ')$');

      // matches class selectors
      reClass = RegExp('(?:\\[[\\x20\\t\\n\\r\\f]*class\\b|\\.' + identifier + ')');

      Optimize = {
        ID: RegExp('^\\*?#(' + identifier + ')|' + skip_groups),
        TAG: RegExp('^(' + identifier + ')|' + skip_groups),
        CLASS: RegExp('^\\.(' + identifier + '$)|' + skip_groups)
      };

      Patterns.id = RegExp('^#(' + identifier + ')(.*)');
      Patterns.tagName = RegExp('^(' + identifier + ')(.*)');
      Patterns.className = RegExp('^\\.(' + identifier + ')(.*)');
      Patterns.attribute = RegExp('^\\[' + attrmatcher + '\\](.*)');

      Tokens.identifier = identifier;
      Tokens.attributes = attributes;

      // validator for complex selectors in ':not()' pseudo-classes
      extendedValidator = standardValidator.replace(pseudoclass, '.*');

      // validator for standard selectors as default
      reValidator = RegExp(standardValidator);
    },

  // code string reused to build compiled functions
  ACCEPT_NODE = 'r[r.length]=c[k];if(f&&false===f(c[k]))break main;else continue main;',

  // compile a comma separated group of selector
  // @mode boolean true for select, false for match
  // return a compiled function
  compile =
    function(selector, source, mode) {

      var parts = typeof selector == 'string' ? selector.match(reSplitGroup) : selector;

      // ensures that source is a string
      typeof source == 'string' || (source = '');

      if (parts.length == 1) {
        source += compileSelector(parts[0], mode ? ACCEPT_NODE : 'f&&f(k);return true;', mode);
      } else {
        // for each selector in the group
        var i = -1, seen = { }, token;
        while ((token = parts[++i])) {
          token = token.replace(reTrimSpaces, '');
          // avoid repeating the same token
          // in comma separated group (p, p)
          if (!seen[token] && (seen[token] = true)) {
            source += compileSelector(token, mode ? ACCEPT_NODE : 'f&&f(k);return true;', mode);
          }
        }
      }

      if (mode) {
        // for select method
        return Function('c,s,d,h,g,f',
          'var N,n,x=0,k=-1,e,r=[];main:while((e=c[++k])){' + source + '}return r;');
      } else {
        // for match method
        return Function('e,s,d,h,g,f',
          'var N,n,x=0,k=e;' + source + 'return false;');
      }
    },

  // compile a CSS3 string selector into ad-hoc javascript matching function
  // @return string (to be compiled)
  compileSelector =
    function(selector, source, mode) {

      var a, b, n, k = 0, expr, match, result, status, test, type;

      while (selector) {

        k++;

        // *** Universal selector
        // * match all (empty block, do not remove)
        if ((match = selector.match(Patterns.universal))) {
          // do nothing, handled in the compiler where
          // BUGGY_GEBTN return comment nodes (ex: IE)
          expr = '';
        }

        // *** ID selector
        // #Foo Id case sensitive
        else if ((match = selector.match(Patterns.id))) {
          // document can contain conflicting elements (id/name)
          // prototype selector unit need this method to recover bad HTML forms
          match[1] = (/\\/).test(match[1]) ? convertEscapes(match[1]) : match[1];
          source = 'if(' + (XML_DOCUMENT ?
            's.getAttribute(e,"id")' :
            '(e.submit?s.getAttribute(e,"id"):e.id)') +
            '=="' + match[1] + '"' +
            '){' + source + '}';
        }

        // *** Type selector
        // Foo Tag (case insensitive)
        else if ((match = selector.match(Patterns.tagName))) {
          // both tagName and nodeName properties may be upper/lower case
          // depending on their creation NAMESPACE in createElementNS()
          test = Config.SVG_LCASE ? '||e.nodeName=="' + match[1].toLowerCase() + '"' : '';
          source = 'if(e.nodeName' + (XML_DOCUMENT ?
            '=="' + match[1] + '"' : '.toUpperCase()' +
            '=="' + match[1].toUpperCase() + '"' + test) +
            '){' + source + '}';
        }

        // *** Class selector
        // .Foo Class (case sensitive)
        else if ((match = selector.match(Patterns.className))) {
          // W3C CSS3 specs: element whose "class" attribute has been assigned a
          // list of whitespace-separated values, see section 6.4 Class selectors
          // and notes at the bottom; explicitly non-normative in this specification.
          match[1] = (/\\/).test(match[1]) ? convertEscapes(match[1]) : match[1];
          match[1] = QUIRKS_MODE ? match[1].toLowerCase() : match[1];
          source = 'if((n=' + (XML_DOCUMENT ?
            's.getAttribute(e,"class")' : 'e.className') +
            ')&&n.length&&(" "+' + (QUIRKS_MODE ? 'n.toLowerCase()' : 'n') +
            '.replace(/' + whitespace + '+/g," ")+" ").indexOf(" ' + match[1] + ' ")>-1' +
            '){' + source + '}';
        }

        // *** Attribute selector
        // [attr] [attr=value] [attr="value"] [attr='value'] and !=, *=, ~=, |=, ^=, $=
        // case sensitivity is treated differently depending on the document type (see map)
        else if ((match = selector.match(Patterns.attribute))) {

          // xml namespaced attribute ?
          expr = match[1].split(':');
          expr = expr.length == 2 ? expr[1] : expr[0] + '';

          if (match[2] && !Operators[match[2]]) {
            emit('Unsupported operator in attribute selectors "' + selector + '"');
            return '';
          }

          test = 'false';

          // replace Operators parameter if needed
          if (match[2] && match[4] && (test = Operators[match[2]])) {
            match[4] = (/\\/).test(match[4]) ? convertEscapes(match[4]) : match[4];
            // case treatment depends on document type
            type = match[5] == 'i' || HTML_TABLE[expr.toLowerCase()];
            test = test.replace(/\%m/g, type ? match[4].toLowerCase() : match[4]);
          } else if (match[2] == '!=' || match[2] == '=') {
            test = 'n' + match[2] + '=""';
          }

          source = 'if(n=s.hasAttribute(e,"' + match[1] + '")){' +
            (match[2] ? 'n=s.getAttribute(e,"' + match[1] + '")' : '') +
            (type && match[2] ? '.toLowerCase();' : ';') +
            'if(' + (match[2] ? test : 'n') + '){' + source + '}}';

        }

        // *** Adjacent sibling combinator
        // E + F (F adiacent sibling of E)
        else if ((match = selector.match(Patterns.adjacent))) {
          source = NATIVE_TRAVERSAL_API ?
            'var N' + k + '=e;if((e=e.previousElementSibling)){' + source + '}e=N' + k + ';' :
            'var N' + k + '=e;while((e=e.previousSibling)){if(e.nodeType==1){' + source + 'break;}}e=N' + k + ';';
        }

        // *** General sibling combinator
        // E ~ F (F relative sibling of E)
        else if ((match = selector.match(Patterns.relative))) {
          source = NATIVE_TRAVERSAL_API ?
            'var N' + k + '=e;while((e=e.previousElementSibling)){' + source + '}e=N' + k + ';' :
            'var N' + k + '=e;while((e=e.previousSibling)){if(e.nodeType==1){' + source + '}}e=N' + k + ';';
        }

        // *** Child combinator
        // E > F (F children of E)
        else if ((match = selector.match(Patterns.children))) {
          source = 'var N' + k + '=e;if((e=e.parentNode)&&e.nodeType==1){' + source + '}e=N' + k + ';';
        }

        // *** Descendant combinator
        // E F (E ancestor of F)
        else if ((match = selector.match(Patterns.ancestor))) {
          source = 'var N' + k + '=e;while((e=e.parentNode)&&e.nodeType==1){' + source + '}e=N' + k + ';';
        }

        // *** Structural pseudo-classes
        // :root, :empty,
        // :first-child, :last-child, :only-child,
        // :first-of-type, :last-of-type, :only-of-type,
        // :nth-child(), :nth-last-child(), :nth-of-type(), :nth-last-of-type()
        else if ((match = selector.match(Patterns.spseudos)) && match[1]) {

          switch (match[1]) {
            case 'root':
              // element root of the document
              if (match[3]) {
                source = 'if(e===h||s.contains(h,e)){' + source + '}';
              } else {
                source = 'if(e===h){' + source + '}';
              }
              break;

            case 'empty':
              // element that has no children
              source = 'if(s.isEmpty(e)){' + source + '}';
              break;

            default:
              if (match[1] && match[2]) {
                if (match[2] == 'n') {
                  source = 'if(e!==h){' + source + '}';
                  break;
                } else if (match[2] == 'even') {
                  a = 2;
                  b = 0;
                } else if (match[2] == 'odd') {
                  a = 2;
                  b = 1;
                } else {
                  // assumes correct "an+b" format, "b" before "a" to keep "n" values
                  b = ((n = match[2].match(/(-?\d+)$/)) ? parseInt(n[1], 10) : 0);
                  a = ((n = match[2].match(/(-?\d*)n/i)) ? parseInt(n[1], 10) : 0);
                  if (n && n[1] == '-') a = -1;
                }

                // build test expression out of structural pseudo (an+b) parameters
                // see here: http://www.w3.org/TR/css3-selectors/#nth-child-pseudo
                test = a > 1 ?
                  (/last/i.test(match[1])) ? '(n-(' + b + '))%' + a + '==0' :
                  'n>=' + b + '&&(n-(' + b + '))%' + a + '==0' : a < -1 ?
                  (/last/i.test(match[1])) ? '(n-(' + b + '))%' + a + '==0' :
                  'n<=' + b + '&&(n-(' + b + '))%' + a + '==0' : a === 0 ?
                  'n==' + b : a == -1 ? 'n<=' + b : 'n>=' + b;

                // 4 cases: 1 (nth) x 4 (child, of-type, last-child, last-of-type)
                source =
                  'if(e!==h){' +
                    'n=s[' + (/-of-type/i.test(match[1]) ? '"nthOfType"' : '"nthElement"') + ']' +
                      '(e,' + (/last/i.test(match[1]) ? 'true' : 'false') + ');' +
                    'if(' + test + '){' + source + '}' +
                  '}';

              } else {
                // 6 cases: 3 (first, last, only) x 1 (child) x 2 (-of-type)
                a = /first/i.test(match[1]) ? 'previous' : 'next';
                n = /only/i.test(match[1]) ? 'previous' : 'next';
                b = /first|last/i.test(match[1]);

                type = /-of-type/i.test(match[1]) ? '&&n.nodeName!=e.nodeName' : '&&n.nodeName<"@"';

                source = 'if(e!==h){' +
                  ( 'n=e;while((n=n.' + a + 'Sibling)' + type + ');if(!n){' + (b ? source :
                    'n=e;while((n=n.' + n + 'Sibling)' + type + ');if(!n){' + source + '}') + '}' ) + '}';
              }
              break;
          }

        }

        // *** negation, user action and target pseudo-classes
        // *** UI element states and dynamic pseudo-classes
        // CSS4 :matches 
        // CSS3 :not, :checked, :enabled, :disabled, :target
        // CSS3 :active, :hover, :focus
        // CSS3 :link, :visited
        else if ((match = selector.match(Patterns.dpseudos)) && match[1]) {

          switch (match[1].match(/^\w+/)[0]) {
            // CSS4 matches pseudo-class
            case 'matches':
              expr = match[3].replace(reTrimSpaces, '');
              source = 'if(s.match(e, "' + expr.replace(/\x22/g, '\\"') + '",g)){' + source +'}';
              break;

            // CSS3 negation pseudo-class
            case 'not':
              // compile nested selectors, DO NOT pass the callback parameter
              // SIMPLENOT allow disabling complex selectors nested
              // in ':not()' pseudo-classes, breaks some test units
              expr = match[3].replace(reTrimSpaces, '');

              if (Config.SIMPLENOT && !reSimpleNot.test(expr)) {
                // see above, log error but continue execution
                emit('Negation pseudo-class only accepts simple selectors "' + selector + '"');
                return '';
              } else {
                if ('compatMode' in doc) {
                  source = 'if(!' + compile(expr, '', false) + '(e,s,d,h,g)){' + source + '}';
                } else {
                  source = 'if(!s.match(e, "' + expr.replace(/\x22/g, '\\"') + '",g)){' + source +'}';
                }
              }
              break;

            // CSS3 UI element states
            case 'checked':
              // for radio buttons checkboxes (HTML4) and options (HTML5)
              source = 'if((typeof e.form!=="undefined"&&(/^(?:radio|checkbox)$/i).test(e.type)&&e.checked)' +
                (Config.USE_HTML5 ? '||(/^option$/i.test(e.nodeName)&&(e.selected||e.checked))' : '') +
                '){' + source + '}';
              break;
            case 'disabled':
              // does not consider hidden input fields
              source = 'if(((typeof e.form!=="undefined"' +
                (Config.USE_HTML5 ? '' : '&&!(/^hidden$/i).test(e.type)') +
                ')||s.isLink(e))&&e.disabled===true){' + source + '}';
              break;
            case 'enabled':
              // does not consider hidden input fields
              source = 'if(((typeof e.form!=="undefined"' +
                (Config.USE_HTML5 ? '' : '&&!(/^hidden$/i).test(e.type)') +
                ')||s.isLink(e))&&e.disabled===false){' + source + '}';
              break;

            // CSS3 lang pseudo-class
            case 'lang':
              test = '';
              if (match[2]) test = match[2].substr(0, 2) + '-';
              source = 'do{(n=e.lang||"").toLowerCase();' +
                'if((n==""&&h.lang=="' + match[2].toLowerCase() + '")||' +
                '(n&&(n=="' + match[2].toLowerCase() +
                '"||n.substr(0,3)=="' + test.toLowerCase() + '")))' +
                '{' + source + 'break;}}while((e=e.parentNode)&&e!==g);';
              break;

            // CSS3 target pseudo-class
            case 'target':
              source = 'if(e.id==d.location.hash.slice(1)){' + source + '}';
              break;

            // CSS3 dynamic pseudo-classes
            case 'link':
              source = 'if(s.isLink(e)&&!e.visited){' + source + '}';
              break;
            case 'visited':
              source = 'if(s.isLink(e)&&e.visited){' + source + '}';
              break;

            // CSS3 user action pseudo-classes IE & FF3 have native support
            // these capabilities may be emulated by some event managers
            case 'active':
              if (XML_DOCUMENT) break;
              source = 'if(e===d.activeElement){' + source + '}';
              break;
            case 'hover':
              if (XML_DOCUMENT) break;
              source = 'if(e===d.hoverElement){' + source + '}';
              break;
            case 'focus':
              if (XML_DOCUMENT) break;
              source = NATIVE_FOCUS ?
                'if(e===d.activeElement&&d.hasFocus()&&(e.type||e.href||typeof e.tabIndex=="number")){' + source + '}' :
                'if(e===d.activeElement&&(e.type||e.href)){' + source + '}';
              break;

            // CSS2 selected pseudo-classes, not part of current CSS3 drafts
            // the 'selected' property is only available for option elements
            case 'selected':
              // fix Safari selectedIndex property bug
              expr = BUGGY_SELECTED ? '||(n=e.parentNode)&&n.options[n.selectedIndex]===e' : '';
              source = 'if(/^option$/i.test(e.nodeName)&&(e.selected||e.checked' + expr + ')){' + source + '}';
              break;

            default:
              break;
          }

        }

        else if ((match = selector.match(Patterns.epseudos)) && match[1]) {
          source = 'if(!(/1|11/).test(e.nodeType)){' + source + '}';
        }

        else {

          // this is where external extensions are
          // invoked if expressions match selectors
          expr = false;
          status = false;
          for (expr in Selectors) {
            if ((match = selector.match(Selectors[expr].Expression)) && match[1]) {
              result = Selectors[expr].Callback(match, source);
              if ('match' in result) { match = result.match; }
              source = result.source;
              status = result.status;
              if (status) { break; }
            }
          }

          // if an extension fails to parse the selector
          // it must return a false boolean in "status"
          if (!status) {
            // log error but continue execution, don't throw real exceptions
            // because blocking following processes maybe is not a good idea
            emit('Unknown pseudo-class selector "' + selector + '"');
            return '';
          }

          if (!expr) {
            // see above, log error but continue execution
            emit('Unknown token in selector "' + selector + '"');
            return '';
          }

        }

        // error if no matches found by the pattern scan
        if (!match) {
          emit('Invalid syntax in selector "' + selector + '"');
          return '';
        }

        // ensure "match" is not null or empty since
        // we do not throw real DOMExceptions above
        selector = match && match[match.length - 1];
      }

      return source;
    },

  /*----------------------------- QUERY METHODS ------------------------------*/

  // match element with selector
  // @return boolean
  match =
    function(element, selector, from, callback) {

      var parts;

      if (!(element && element.nodeType == 1)) {
        emit('Invalid element argument');
        return false;
      } else if (typeof selector != 'string') {
        emit('Invalid selector argument');
        return false;
      } else if (from && from.nodeType == 1 && !contains(from, element)) {
        return false;
      } else if (lastContext !== from) {
        // reset context data when it changes
        // and ensure context is set to a default
        switchContext(from || (from = element.ownerDocument));
      }

      // normalize the selector string, remove [\n\r\f]
      // whitespace, replace codepoints 0 with '\ufffd'
      // trim non-relevant leading/trailing whitespaces
      selector = selector.
        replace(reTrimSpaces, '').
        replace(/\x00|\\$/g, '\ufffd');

      Config.SHORTCUTS && (selector = Dom.shortcuts(selector, element, from));

      if (lastMatcher != selector) {
        // process valid selector strings
        if ((parts = selector.match(reValidator)) && parts[0] == selector) {
          isSingleMatch = (parts = selector.match(reSplitGroup)).length < 2;
          // save passed selector
          lastMatcher = selector;
          lastPartsMatch = parts;
        } else {
          emit('The string "' + selector + '", is not a valid CSS selector');
          return false;
        }
      } else parts = lastPartsMatch;

      // compile matcher resolvers if necessary
      if (!matchResolvers[selector] || matchContexts[selector] !== from) {
        matchResolvers[selector] = compile(isSingleMatch ? [selector] : parts, '', false);
        matchContexts[selector] = from;
      }

      return matchResolvers[selector](element, Snapshot, doc, root, from, callback);
    },

  // select only the first element
  // matching selector (document ordered)
  first =
    function(selector, from) {
      return select(selector, from, function() { return false; })[0] || null;
    },

  // select elements matching selector
  // using new Query Selector API
  // or cross-browser client API
  // @return array
  select =
    function(selector, from, callback) {

      var i, changed, element, elements, parts, token, original = selector;

      if (arguments.length === 0) {
        emit('Not enough arguments');
        return [ ];
      } else if (typeof selector != 'string') {
        return [ ];
      } else if (from && !(/1|9|11/).test(from.nodeType)) {
        emit('Invalid or illegal context element');
        return [ ];
      } else if (lastContext !== from) {
        // reset context data when it changes
        // and ensure context is set to a default
        switchContext(from || (from = doc));
      }

      if (Config.CACHING && (elements = Dom.loadResults(original, from, doc, root))) {
        return callback ? concatCall([ ], elements, callback) : elements;
      }

      // normalize the selector string, remove [\n\r\f]
      // whitespace, replace codepoints 0 with '\ufffd'
      // trim non-relevant leading/trailing whitespaces
      selector = selector.
        replace(reTrimSpaces, '').
        replace(/\x00|\\$/g, '\ufffd');

      if (!OPERA_QSAPI && reSimpleSelector.test(selector)) {
        switch (selector.charAt(0)) {
          case '#':
            if (Config.UNIQUE_ID) {
              elements = (element = _byId(selector.slice(1), from)) ? [ element ] : [ ];
            }
            break;
          case '.':
            elements = _byClass(selector.slice(1), from);
            break;
          default:
            elements = _byTag(selector, from);
            break;
        }
      }

      else if (!XML_DOCUMENT && Config.USE_QSAPI &&
        !(BUGGY_QUIRKS_QSAPI && reClass.test(selector)) &&
        !RE_BUGGY_QSAPI.test(selector)) {
        try {
          elements = from.querySelectorAll(selector);
        } catch(e) { }
      }

      if (elements) {
        elements = callback ? concatCall([ ], elements, callback) :
          NATIVE_SLICE_PROTO ? slice.call(elements) : concatList([ ], elements);
        Config.CACHING && Dom.saveResults(original, from, doc, elements);
        return elements;
      }

      Config.SHORTCUTS && (selector = Dom.shortcuts(selector, from));

      if ((changed = lastSelector != selector)) {
        // process valid selector strings
        if ((parts = selector.match(reValidator)) && parts[0] == selector) {
          isSingleSelect = (parts = selector.match(reSplitGroup)).length < 2;
          // save passed selector
          lastSelector = selector;
          lastPartsSelect = parts;
        } else {
          emit('The string "' + selector + '", is not a valid CSS selector');
          return [ ];
        }
      } else parts = lastPartsSelect;

      // commas separators are treated sequentially to maintain order
      if (from.nodeType == 11) {

        elements = byTagRaw('*', from);

      } else if (!XML_DOCUMENT && isSingleSelect) {

        if (changed) {
          // get right most selector token
          parts = selector.match(reSplitToken);
          token = parts[parts.length - 1];

          // only last slice before :not rules
          lastSlice = token.split(':not');
          lastSlice = lastSlice[lastSlice.length - 1];

          // position where token was found
          lastPosition = selector.length - token.length;
        }

        // ID optimization RTL, to reduce number of elements to visit
        if (Config.UNIQUE_ID && lastSlice && (parts = lastSlice.match(Optimize.ID)) && (token = parts[1])) {
          if ((element = _byId(token, from))) {
            if (match(element, selector)) {
              callback && callback(element);
              elements = [element];
            } else elements = [ ];
          }
        }

        // ID optimization LTR, to reduce selection context searches
        else if (Config.UNIQUE_ID && (parts = selector.match(Optimize.ID)) && (token = parts[1])) {
          if ((element = _byId(token, doc))) {
            if ('#' + token == selector) {
              callback && callback(element);
              elements = [element];
            } else if (/[>+~]/.test(selector)) {
              from = element.parentNode;
            } else {
              from = element;
            }
          } else elements = [ ];
        }

        if (elements) {
          Config.CACHING && Dom.saveResults(original, from, doc, elements);
          return elements;
        }

        if (!NATIVE_GEBCN && lastSlice && (parts = lastSlice.match(Optimize.TAG)) && (token = parts[1])) {
          if ((elements = _byTag(token, from)).length === 0) { return [ ]; }
          selector = selector.slice(0, lastPosition) + selector.slice(lastPosition).replace(token, '*');
        }

        else if (lastSlice && (parts = lastSlice.match(Optimize.CLASS)) && (token = parts[1])) {
          if ((elements = _byClass(token, from)).length === 0) { return [ ]; }
          selector = selector.slice(0, lastPosition) + selector.slice(lastPosition).replace('.' + token,
            reOptimizeSelector.test(selector.charAt(selector.indexOf(token) - 1)) ? '' : '*');
        }

        else if ((parts = selector.match(Optimize.CLASS)) && (token = parts[1])) {
          if ((elements = _byClass(token, from)).length === 0) { return [ ]; }
          for (i = 0, els = [ ]; elements.length > i; ++i) {
            els = concatList(els, elements[i].getElementsByTagName('*'));
          }
          elements = els;
          selector = selector.slice(0, lastPosition) + selector.slice(lastPosition).replace('.' + token,
            reOptimizeSelector.test(selector.charAt(selector.indexOf(token) - 1)) ? '' : '*');
        }

        else if (NATIVE_GEBCN && lastSlice && (parts = lastSlice.match(Optimize.TAG)) && (token = parts[1])) {
          if ((elements = _byTag(token, from)).length === 0) { return [ ]; }
          selector = selector.slice(0, lastPosition) + selector.slice(lastPosition).replace(token, '*');
        }

      }

      if (!elements) {
        if (IE_LT_9) {
          elements = /^(?:applet|object)$/i.test(from.nodeName) ? from.children : byTagRaw('*', from);
        } else {
          elements = from.getElementsByTagName('*');
        }
      }
      // end of prefiltering pass

      // compile selector resolver if necessary
      if (!selectResolvers[selector] || selectContexts[selector] !== from) {
        selectResolvers[selector] = compile(isSingleSelect ? [selector] : parts, '', true);
        selectContexts[selector] = from;
      }

      elements = selectResolvers[selector](elements, Snapshot, doc, root, from, callback);

      Config.CACHING && Dom.saveResults(original, from, doc, elements);

      return elements;
    },

  /*-------------------------------- STORAGE ---------------------------------*/

  // empty function handler
  FN = function(x) { return x; },

  // compiled match functions returning booleans
  matchContexts = { },
  matchResolvers = { },

  // compiled select functions returning collections
  selectContexts = { },
  selectResolvers = { },

  // used to pass methods to compiled functions
  Snapshot = {

    // element indexing methods
    nthElement: nthElement,
    nthOfType: nthOfType,

    // element inspection methods
    getAttribute: getAttribute,
    hasAttribute: hasAttribute,

    // element selection methods
    byClass: _byClass,
    byName: byName,
    byTag: _byTag,
    byId: _byId,

    // helper/check methods
    contains: contains,
    isEmpty: isEmpty,
    isLink: isLink,

    // selection/matching
    select: select,
    match: match
  },

  /*------------------------------- PUBLIC API -------------------------------*/

  // code referenced by extensions
  Dom = {

    ACCEPT_NODE: ACCEPT_NODE,

    // retrieve element by id attr
    byId: byId,

    // retrieve elements by tag name
    byTag: byTag,

    // retrieve elements by name attr
    byName: byName,

    // retrieve elements by class name
    byClass: byClass,

    // read the value of the attribute
    // as was in the original HTML code
    getAttribute: getAttribute,

    // check for the attribute presence
    // as was in the original HTML code
    hasAttribute: hasAttribute,

    // element match selector, return boolean true/false
    match: match,

    // first element match only, return element or null
    first: first,

    // elements matching selector, starting from element
    select: select,

    // compile selector into ad-hoc javascript resolver
    compile: compile,

    // check that two elements are ancestor/descendant
    contains: contains,

    // handle selector engine configuration settings
    configure: configure,

    // initialize caching for each document
    setCache: FN,

    // load previously collected result set
    loadResults: FN,

    // save previously collected result set
    saveResults: FN,

    // handle missing context in selector strings
    shortcuts: FN,

    // log resolvers errors/warnings
    emit: emit,

    // options enabing specific engine functionality
    Config: Config,

    // pass methods references to compiled resolvers
    Snapshot: Snapshot,

    // operators descriptor
    // for attribute operators extensions
    Operators: Operators,

    // selectors descriptor
    // for pseudo-class selectors extensions
    Selectors: Selectors,

    // export validators REs
    Tokens: Tokens,

    // export version string
    Version: version,

    // add or overwrite user defined operators
    registerOperator:
      function(symbol, resolver) {
        Operators[symbol] || (Operators[symbol] = resolver);
      },

    // add selector patterns for user defined callbacks
    registerSelector:
      function(name, rexp, func) {
        Selectors[name] || (Selectors[name] = {
          Expression: rexp,
          Callback: func
        });
      }

  };

  /*---------------------------------- INIT ----------------------------------*/

  // init context specific variables
  initialize(doc);

  return Dom;
});
