HTML-mode tags not recognized

[Devin Prater]

Hi all. I’ve recently started using html-mode, nhtml-mode and such. It works 
very well, better than any other editor I’ve used. The only tag that I use that 
isn’t recognized is <aside> and </aside>
The aside tag denotes a “complimentary” landmark, useful for users of assistive 
technologies, like screen readers, to put content into a sort of footnote 
region. Is there a way I can get this to be recognized? I think FlyCheck is 
responsible for the hints I get in HTML-mode, and I’ve looked at customize for 
that, but haven’t found any way to add <aside> to it. Complicating things 
slightly is the fact that in the list of tags gotten with C-C C-T does have the 
aside tag.
So, any help with this would be appreciated. It isn’t that big of a deal, but 
having html-tidy finish successfully would be nice.