But what's ERT?

Some ideas:

• last time I looked it had about 9000 lines, so my first approach works be to divide and conquer into smaller modules.
• some Elisp code should be generated from Perl. (Lispers will kill me) For instance a large chunk is made of help docs dating back from Perl 4
• Ilya always wanted to be backwards compatible with emacs 18 or 19 which didn't have a very fancy parsing tech. Consider dropping that Code.
• you'll need a test suite, preferably written in Perl too.