Just a fun little project for my Sunday afternoon:
http://www.mediawiki.org/wiki/Preprocessor_ABNF
Turns out the production rules are pretty simple. The magic is in the disambiguation. An EBNF representation of the whole of MediaWiki wikitext, if such a thing is possible, would only go a small way towards specifying the language.
-- Tim Starling
wikitech-l@lists.wikimedia.org