I'm going to have a try at sticking this lot into the ERE. The description looks pretty good, so I'm going to put it in mostly as-is, just tidying up bits where it makes sense for the wiki.

Edit: done the three file specifications (see J2A File Format, J2L File Format and J2T File Format). I'm just about to add the zlib info.

Edit: zlib done. These pages need to be linked into the main wiki, but should do for now.