I'm curious about the backend for WYSIWYG editors (specifically librewriter and MS Word).
I know that you can produce fancy and nicely typeset documents using LaTeX, TeX and HTML+CSS. I was wondering if any of these markup languages (or something similar) underlies popular word processing software packages?
There are several sites with useful information about the OOXML file format. OfficeOpenXML has the most verbose explanations of OOXML. Other sites, like datypic.com and c-rex.net are mostly repackagings of the ECMA specs in a more readable form. I write about OOXML from the point of view of useful techniques for common Office problems: OOXML Hacking: Locking Graphics