Sets the XData of this object. 

The sublist for each RegApp, and the ResBuf list itself, must begin with a ResBuf with resbuf.restype == kDxfRegAppName and resbuf.rstring == a valid regAppName string. 

Any existing XData for the specified regAppName will be replaced. 

To remove the regAppName and its XData, just provide the regAppName with no data. 

If you override this method, you should supermessage this classes parent class to add add the XData to the object.