Couldn't locate the OP but when I saw these english contractions somewhere in another forum it got me thinking...
... wouldn't it be great
polishing further the book and replacing full words by their contractions (even better, using contractions specific to language of the book)?
I've also seen there's controversies about using contractions. FWIW, I don't natively speak english, but maybe others would like this feature too.
Anyway, tanx 10⁶ for your great plugin, I use it all the time for the smart quotes.