Bootstrap und CSS Validation
Generally speaking, we don’t worry about W3C validation.
Practically speaking, it honestly doesn’t make much sense to strive for it in most production environments if industry accepted practices are viewed as errors. All the CSS we use is valid, and while some lines are hacks (* for IE7, 9 for IE7-9, etc), it all renders as expected. I’m sure much of this will be cleaned up as we drop legacy browser support (I see lots of hiccups for the IE hacks).