I didn’t realise we’d entered a time machine to 2007. I’ve worked extensively with OOXML and yes, the documentation is cryptic and often absent, but Microsoft will help you out if you contact them on their forums. I see Libre Office devs there all the time!

But the complexity is not some kind of conspiracy - it’s inherent - it comes from the fact that Office is ancient and very, very complex with a huge number of features. Many features are implemented in backwards compatible way on top of the old version of similar features and then the whole thing has been back ported from a bunch of C structure to XML which has the most woeful and underpowered schema language imaginable.