code: function mxCellMarker(graph, validColor, invalidColor, hotspot)
  {
  	mxEventSource.call(this);
  	
  	if (graph != null)
  	{
  		this.graph = graph;
  		this.validColor = (validColor != null) ? validColor : mxConstants.DEFAULT_VALID_COLOR;
  		this.invalidColor = (invalidColor != null) ? invalidColor : mxConstants.DEFAULT_INVALID_COLOR;
  		this.hotspot = (hotspot != null) ? hotspot : mxConstants.DEFAULT_HOTSPOT;
  		
  		this.highlight = new mxCellHighlight(graph);
  	}
  }
docs: Copyright (c) 2006-2015, JGraph Ltd
  Copyright (c) 2006-2015, Gaudenz Alder
   
  Class: mxCellMarker
  
  A helper class to process mouse locations and highlight cells.
  
  Helper class to highlight cells. To add a cell marker to an existing graph
  for highlighting all cells, the following code is used:
  
  (code)
  var marker = new mxCellMarker(graph);
  graph.addMouseListener({
  mouseDown: function() {},
  mouseMove: function(sender, me)
  {
  marker.process(me);
  },
  mouseUp: function() {}
  });
  (end)
  
  Event: mxEvent.MARK
  
  Fires after a cell has been marked or unmarked. The <code>state</code>
  property contains the marked <mxCellState> or null if no state is marked.
  
  Constructor: mxCellMarker
  
  Constructs a new cell marker.
  
  Parameters:
  
  graph - Reference to the enclosing <mxGraph>.
  validColor - Optional marker color for valid states. Default is
  <mxConstants.DEFAULT_VALID_COLOR>.
  invalidColor - Optional marker color for invalid states. Default is
  <mxConstants.DEFAULT_INVALID_COLOR>.
  hotspot - Portion of the width and hight where a state intersects a
  given coordinate pair. A value of 0 means always highlight. Default is
  <mxConstants.DEFAULT_HOTSPOT>.