I'm not going to beleaguer the point (I'm not one to do much font embedding in the first place), but it does seem a little drastic to throw a font out on such a technical definition of "being used." It renders in ADE, Adobe's RMSDK, Sigil and calibre, so the font is clearly "being used" (even if it's being used improperly).
It just seems odd to me that doing nothing other than
removing "font-weight: bold" from the "first-words" class, makes your plugin believe the font is suddenly being used (with no change to the @font-face declaration) ... and that adding the line back in renders the font "unused" once again.
I do understand the technical distinction, but it doesn't seem appropriate to me to delete font files (and their accompanying css references) that are, in fact, being used.
Inappropriately perhaps, but "used" nonetheless.
If
I were doing it, "used" would mean: a font-face declaration; the font-family being used in a class selector; and that class being applied to elements in the (x)html that contain text. But in the end ... it's your plugin.
