> I didn't know W3Schools was so bad.

Yeah, again, it's not so bad now as stated back then on W3Fools (which is a bit outdated). But I better trust other documentation sources than a one that spends $$ on SEO that should have spent on documentation :)

> Since we can't know the intent, maybe leave it as 
 but add a style="text-decoration: line-through;"?

well, `s` is already styled as strike-through by default, so I don't think we need inline styling here.