It is actually quite useful to have the choice between a clearfix that uses pseudo-elements and one that does not. Pseudo-elements are used regularly for other purposes these days. 

For the same reason, I'm hesitant to include the `:before` hacks, when only `:after` is actually needed for clearing floats. I know some people like to un-collapse their top margins, but that seems like a separate issue to me. Margins are supposed to collapse, and I don't want that changing just because I need my floats cleared.

Maybe we need some optional defaults and arguments here?