(plus minor heading/prose tweak). See https://twitter.com/thierrykoblentz/status/654707875869122560 for context (though discussion there suggest a different solution - doubling up aria-label and title - which I'm not sure would fly).
reason for removing the <span> (rather than removing the aria-label) is that we seem to be favoring the latter in other parts of the docs.
/cc @cvrebert @mdo