docs: function keydown( event ) {
  
  		if ( _this.enabled === false ) return;
  
  		window.removeEventListener( 'keydown', keydown );
  
  		_prevState = _state;
  
  		if ( _state !== STATE.NONE ) {
  
  			return;
  
  		} else if ( event.keyCode === _this.keys[ STATE.ROTATE ] && !_this.noRotate ) {
  
  			_state = STATE.ROTATE;
  
  		} else if ( event.keyCode === _this.keys[ STATE.ZOOM ] && !_this.noZoom ) {
  
  			_state = STATE.ZOOM;
  
  		} else if ( event.keyCode === _this.keys[ STATE.PAN ] && !_this.noPan ) {
  
  			_state = STATE.PAN;
  
  		}
  
  	}