As an aside before I start work on belatedly fixing some of unicode-math’s more pressing shortcomings, I’ve also started work tidying up the breqn package:

The breqn package was the brainchild of Michael J. Downes (of amsmath fame), and later updated by Morten Høgholm as part of his honours thesis. The package is explained in Michael’s 1997 TUGboat article ‘Breaking Equations’, and Morten’s thesis is available online if you know where to look (I don’t know how long it will be available there).

Since I have so much trouble keeping up with LaTeX work as it is, why would I take another package under my belt? In short, partly because breqn vastly alters the implementation of LaTeX mathematics, so I need to eventually know how to hook into it to properly support unicode-math. But also partly because of its heritage; such a promising piece of work shouldn’t be neglected—I used breqn in my own PhD thesis, and while I could have done without it, once you start with breqn it is hard to go back to amsmath.

If you’re interested, I need help generating test files; once they’re sufficiently comprehensive I’ll begin the process of translating the code into LaTeX3. Hopefully I can fix a bug or two along the way.