SIE is a tagged text file format, not XML like XBRL GL and UN/CEFACT accounting.
However the SIE file format works with any charts of accounts and is technically independent of BAS.
As a vendor interest group SIE is not bound to the statements of neutrality against proprietary solutions of regular standards organisations.
That makes the SIE specification also include implementation instruction layer that is not possible in official standards organisations work.
The implementation instruction layer has helped a lot in limiting dialects and makes certain the information interchange work in practice.