Well, we should definitely get latexmk going. Looks like the "latexmkrc" file needs a setting for "makeindex", pointing to xindy instead. And yes, that will be used for all indexes, not just the grammar index.

I've updated the latexmkrc config file so that it runs xindy. I also modified it so that it automatically builds with pdfLaTeX and only builds the std.tex file. So you can just run latexmk with no arguments now and it should do the right thing.

I'm currently fixing up the index cross-references. xindy treats cross-references as first-class objects and will report an error if you refer to a nonexistent index entry. As a consequence of this, the argument to the see and seealso entries must match the unformatted main index entry to which it refers. In other words, I'm changing \index{blah|see{something, else}} to \index{blah|see{something!else}}. (Alternatively, I can instruct xindy to not check the cross-references. Personally, I think it's probably worth the initial pain as it makes the index syntax more consistent [i.e., always use entry!subentry] and helps us find dangling references.)

There are a few other odds and ends I'm going to check up on, too. I'll post progress updates as I go and will tidy up the git commit history before the final merge.

I've added a "needs rebase" tag, repurposing it as a general "needs more work" thing.