I'm looking for some good books on XeTeX to have them as references whenever I want to look up something or learn something new. Level doesn't really matter, either novice or advanced would do but I'd really like the book(s) to be broad in content - like some of the LaTeX books that I've read:
A Guide to LaTeX by H. Kopka and P. Daly
The Not So Short Introduction to LATEX2ε by T. Oetiker
Many thanks for any recommendations,