Have you tried them though? Now check it out with kerning and/or italics. Do you see overhanging when you draw the rectangular box found via the API? Good example is strings that end with a character like f.
Works in theory. In practice, it does not. That is what I found but again, I'd be happy to be wrong.
That's interesting, the computed bbox seems to be slightly off on Chrome when I apply "italic" font style.
When working on it a year ago at another employer, we had a list of edge cases. I don't recall them all but some were off by quite a bit. Enough so that the work around was to do everything in SVG except text and use plain DOM position on top for text. That was a bit better. It would be wonderful to do everything in SVG.