code: function mxValueChange(model, cell, value)
  {
  	this.model = model;
  	this.cell = cell;
  	this.value = value;
  	this.previous = value;
  }
docs: Class: mxValueChange
  
  Action to change a user object in a model.
  
  Constructor: mxValueChange
  
  Constructs a change of a user object in the
  specified model.