After having failed to find the incantation before, a slightly different bit of Googling turned up this trick, that saves the needless <span> in IE that I had in the previous entry :
<!--[if IE]><acronym title="???">???</acronym><![endif]--><!--[if !IE]> <--><abbr title="???">???</abbr><!--> <![endif]-->
where I've folded this at necessary whitespace. The <acronym/> is IE only, the <abbr/> is non-IE (or back version IE, which won't know what to do with it...).