A chapter is being worked on for the next edition of the Open Source Architecture ORA book, here:
https://www.mediawiki.org/wiki/MediaWiki_architecture_document/text
I suspect there's some more information about current parser project work that should be in there, but isn't. I'm going to be doing an edit pass on that page tonight or tomorrow, and if there's info you think should be in there you or I should put it in?
Cheers, -- jra