docs: function clearModifier(event){
      var key = event.keyCode, k,
          i = index(_downKeys, key);
  
      // remove key from _downKeys
      if (i >= 0) {
          _downKeys.splice(i, 1);
      }
  
      if(key == 93 || key == 224) key = 91;
      if(key in _mods) {
        _mods[key] = false;
        for(k in _MODIFIERS) if(_MODIFIERS[k] == key) assignKey[k] = false;
      }
    }