With some pride, I can say that, so far as I know, my article is the best documentation there is on Word templates. About 15 or 20 years ago it was copied onto the Microsoft website with my permission, but has not been updated there since.

There is documentation at Microsoft that is not shared with the general public. I believe their MVP volunteers get access to more than the general public, but not to everything.

My article could stand a good rewrite, I know. I am a lawyer, not a coder nor a technical writer. I welcome chances to make it better, though.

The people who design and code Word do not, as far as I know, actually use it. It is a hodgepodge of code and very creaky. The left hand does not know what the right hand is doing. The multiple versions for different platforms adds to the confusion almost exponentially. As far as I can tell, Sharepoint and Word's online and mobile versions do not use templates the way that the desktop versions do. They treat them like documents.