XML-TNS    ::= "<xml-tn header>" [ACK | CMD] XML-TN DESCRIPTION "</xml-tn>"(these are entity updates) 
            |  "<xml-tn header>" ACK XML-MAP DESCRIPTION "</xml-tn>"
            |  "<xml-tn header>" ACK VIEWPORT DESCRIPTION "</xml-tn>"
            |  "<xml-tn header>" ACK DESCRIPTION "</xml-tn>"
            |  "<xml-tn header>" ERROR DESCRIPTION "</xml-tn>"
          			 
ACK        ::= "<ack>previous client command</ack>"

CMD        ::= "<cmd />"  (forced updates without a previous command from the client)

ERROR      ::= "<err>previous client command</err>"

DESCRIPTION::= MSG
            |  MSG ADM
            |  MSG DBG
            |  MSG DBG ADM
            |                   (empty)

MSG        ::= "<msg>" "message for user" "</msg>"

ADM        ::= "<adm>" "administrative message" "</adm>"

DBG        ::= "<dbg>" "debug message" "</dbg>"

XML-TN     ::= [ENTITY]+
            |  [EUPDATE]+               (entity behaviour change) 
            |  [EVCHANGE]+              (entity velocity change)
            |  [ERCHANGE]+              (entity rotation change)
			
ENTITY     ::= "<ent>" ID XY [ BEHAVIOUR [<IMAGE>]* ]* "</ent>"  (entity == ent)

IMG        ::= "<svg src="http://servername:port/path" />"
            |  "<svg>" embedded SVG "</svg>"

EUPDATE    ::= "<ent>" ID BEHAVIOUR "</ent>"

EVCHANGE   ::= "<ent>" ID V "</ent>"

ERCHANGE   ::= "<ent>" ID R "</ent>"

ID         ::= "<id>" UNIQUEID "</id>"

BEHAVIOUR  ::= "<bhr>" string "</bhr>" (bhr == behaviour)

UNIQUEID   ::= integer

XML-MAP    ::= "<map>" 
                   "<dim>" 
                       "<x>"integer"</x>""<y>"integer"</y>"
                   "</dim>" 
				   [ENTITY]* 
               "</map>"

VIEWPORT   ::= "<viewport>" "<x>" integer "</x>" "<y>" integer "</y>" "</viewport>"
								
V          ::= "<v>" float "</v>"  (in m/s)
								
R          ::= "<r>" float "</r>"  (in radians)

XY         ::= "<x>" integer "</x>" "<y>" integer "</y>"