I learned how the win32 common controls combo box worked, which was handy as I had to fix a bug related to it, how they handled compatibility between windows ve

I learned how the win32 common controls combo box worked, which was handy as I had to fix a bug related to it, how they handled compatibility between windows versions and lots of little bits of weird design info in the comments. I spent a good couple of weeks picking interesting bits and analysing them.