yui/yui3 — comment on commit e1d2c90eed2334936210d1e1c6c53a43934ed517
File: src/button/css/cssbutton.css line 7
By derek:

Amazingly IE 6 & 8 are more similar in some cases than IE 7 when it comes to rendering buttons. So during this IE dev session I was targeting IE7 quite a bit. I may have originally attempted to target IE7, then realized I needed 6 as well, so the hacks blended and *+ was the result. It works as intended for IE6/7, but without knowing the exact target & implications, it's of course better to go with something more understood, in this case, *.