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?
Both MS Office and Open/Libre Office use XML for the stored document representation format (see http://www.ecma-international.org/publications/standards/Ecma-376.htm for MSO and https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=office for Open/Libre Office; some of the specs have been republished as ISO standards). Basically, a .docx file is a ZIP archive containing XML files. Though neither of these office suites, being WYSIWYG-era software, started with a markup-based format as native storage format. Well-known text processors based natively on markup/plain text are WordPerfect and IBM SCRIPT/VS (the latter one introducing GML which later was extended to SGML and forming the base for both HTML and XML).
The markup language used by MS Word's DOCX format is covered by Standard ECMA-376 Office Open XML File Formats, aka OOXML. Libre Office can also import and export DOCX.
See also:
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
