Assume that el.className === "foo bar"
Assume that your selector is "DIV.foo.bar"

(' ' + el.className + ' ').match(re) will only have one match - " foo " - because the "\\s" trailing character on "foo" prevents " bar " from being matched

EZ fix is just to make sure the trailing whitespace is not consumed by the regex

All modern browsers seem to support `window.pageXOffset` and `window.pageYOffset`, which are aliases for `window.scrollX` and `window.scrollY`.

IE doesn't seem to have `window.scrollX` and `window.scrollY`.

fixes #302