Xlib isn't just somewhat documented, it's exceptionally well documented.

I'm no fan of X, but the books documenting it were from an era when the UNIX industry was flush with cash and printed technical writing was at its peak.

It pains me to flip through my volumes of printed O'Reilly X books, knowing how much time and care was put into documentation for such a technical abomination.

https://www.oreilly.com/library/view/xlib-reference-manual/9...