The Foundation sees this as a contradiction to the EU’s own interoperability goals. Although XLSX is standardized as OOXML according to ISO/IEC 29500, Microsoft’s implementations often deviate from the specifications. Furthermore, features often change undocumented, which complicates compatibility with open-source software such as LibreOffice.


I remember, only trouble is a lot of people at the time didn’t care or were paid loads of money to not care.
Also the name Office Open XML right at the time OpenOffice was the only one about before oracle came in and fucked it over