Yes, it was only chance I was dealing with this thread on the PC last night (I'm on the tablet now) and had a look at the data on box SWMBO was watching downstairs. I stumbled on the pop-ups.Ah. Those of us using tablets/touch screens don't get the benefit of pop-ups.
Xkcd has a specific workaround for this issue with alt-text. Might it be possible to add that to webif? (I have no idea what is involved in such coding.)