Hi Florian,
Sorry, I wasn't clear. I agree with you entirely. I was just pointing out that you don't do this sort of sizing for most typesetting purposes because it looks ugly, which is why the rendering engines don't do it that way. But what Richard is discussing is clearly an exception to the general rule, and you are absolutely right that it is the “only reasonable thing to do” in this case, even though you wouldn't do it for most other situations.
Speed shouldn't be an issue, since all the engine has to do is check the actual (versus typographically nominal) bounds and use them. It isn't a complex procedure at all, but whether rendering engine developers would see it as a worthwhile one to address since it does require specific handling is another matter. Only they could say whether it is worth their while. My guess is that as HTML is used more and more to create an experience somewhat equivalent to print, we should see issues like this becoming more important.
-Arle
Sic scripsit Florian Rivoal ad Richard Ishida die Tue Feb 17 2015 05:40:02:
> Unlike the music typesetting software mentioned by Arle, since we're only typesetting a single character this way, rather than entire lines, I don't think this will look ugly, but rather think it actually is the only reasonable thing to do, assuming the the concerns with regards to speed or complexity of implementation do not turn out to be blocking issues.