code: function _enableDrag($canvas, data, layer) {
  	var dragHelperEvents, eventName, i;
  	// Only make layer draggable if necessary
  	if (layer.draggable || layer.cursors) {
  
  		// Organize helper events which enable drag support
  		dragHelperEvents = ['mousedown', 'mousemove', 'mouseup'];
  
  		// Bind each helper event to the canvas
  		for (i = 0; i < dragHelperEvents.length; i += 1) {
  			// Use touch events if appropriate
  			eventName = dragHelperEvents[i];
  			// Bind event
  			_addLayerEvent($canvas, data, layer, eventName);
  		}
  		// Indicate that this layer has events bound to it
  		layer._event = true;
  
  	}
  }
docs: Enable drag support for this layer