I was in a used bookstore a few years ago, and ran across a book titled something like "User Interface Design with MOTIF". Well, it had been a power of years since I last touched X-Windows (with intent to draw pixels, anyway) and I started leafing through it.

Looking for user interface examples.

Leaf, leaf, nothing.

Flip, flip, flipflipflip . . . oh, we're at the index. Nothing.

Over 300 pages and no pictures. Zero diagrams. No user interface principles or discussion about good or bad practices. It was all descriptions of APIs. There was nothing about user interface design in there at all.

IMHO, that's all you really need to know about X-Windows.