I sort of am, but only in the very long term. It can start as a tiny type that just holds its own specific special-casing behavior, and then it can grow in complexity as complexity is needed. That said, it may be difficult to predict what behavior is specific to a single HTML specification until one's tried to provide a choice between multiple specs.

I changed the rendering engine to print some tags inline and self-close some tags.

Awesome. :D

For that matter, I didn't know link and meta could have content.

They're not supposed to. (It would be interesting to look at the DOM to see if they can in practice.) I'm talking about when I might potentially want to give them content for a weird browser-specific hack.

The tag object is just a hashtable, you can always hack it and insert whatever custom attributes you want, and then use these as rendering hints in the rendering engine/function.