Thank yo very much for your reply. a quick follow up question, since i am trying to modify some JSON context in the XData Block, how do i do if i want to write something in a specific location ? 

Suppose the XData block like this and i want to change the "info" 's value to {"name" : "Alex "}

Xdata {

    {

          "info" : { "name" : Jeff }

    }

}