code: function (evt) {
          if(this.keyMask == null) {
              return true;
          }
          /* calculate the keyboard modifier mask for this event */
          var keyModifiers =
              (evt.shiftKey ? OpenLayers.Handler.MOD_SHIFT : 0) |
              (evt.ctrlKey  ? OpenLayers.Handler.MOD_CTRL  : 0) |
              (evt.altKey   ? OpenLayers.Handler.MOD_ALT   : 0) |
              (evt.metaKey  ? OpenLayers.Handler.MOD_META  : 0);
      
          /* if it differs from the handler object's key mask,
             bail out of the event handler */
          return (keyModifiers == this.keyMask);
      }
docs: Method: checkModifiers
  Check the keyMask on the handler.  If no <keyMask> is set, this always
  returns true.  If a <keyMask> is set and it matches the combination
  of keys down on an event, this returns true.
  
  Returns:
  {Boolean} The keyMask matches the keys down on an event.