mxUndoManager.prototype.constructor=mxUndoManager;mxUndoManager.prototype.size=null;mxUndoManager.prototype.history=null;mxUndoManager.prototype.indexOfNextAdd=0;mxUndoManager.prototype.isEmpty=function(){return 0==this.history.length};mxUndoManager.prototype.clear=function(){this.history=[];this.indexOfNextAdd=0;this.fireEvent(new mxEventObject(mxEvent.CLEAR))};mxUndoManager.prototype.canUndo=function(){return 0<this.indexOfNextAdd};