Upon reviewing ISPG V3.1 and sample Invoice, I found discrepancy between them.
As per "IATA IS XML Invoice Standard - V 3 1.xls" - "M&U Charge Category - Chargecode" Sheet,
TaxSubType is mandatory, Tax RegisterationID is Legal Field, and TaxText is Recommended for Mail Invoice.
But on XML Sample file "MXMLF01112010030320110114130569.xml", those items are missing.
(Other sample files otherthan Mail, same is found. Tax items are found from only few samples.)
Please advise wheather Tax Items listed above are mandatory or not.