It's not the airport you're expecting but the onward clearance e.g LAM 3A or LAM WELIN TNT DAYNE 2A etc, it was introduced to cut down the controller issuing a clearance, requiring a subsequent readback.
I don't believe there is any EK documentation on it specifically.
Last edited by Eau de Boeing; 16th Jan 2016 at 16:48.
Reason: spelling