louisremi/background-size-polyfill — pull request #24 by tec (2013-07-30 09:26:20+00:00)
Title: expando.backgroundPosition{X,Y} wrong if e.g. set to 'top'

if pos[1] is 'top', positions[pos[1]] evaluates to zero, which is falsy. Then backgroundPositionY will be set to parseFloat("top") / 100 == NaN