The Parsoid Sanitizer (which is a port of the PHP Sanitizer) has various references to the HTML4.x standards. And, there are wikitext dialectical drifts with HTML5 as well. We should migrate everything (even if it is just documentation) over to HTML5 and minimize the dialectical differences as far as possible.

This is a post-port and possibly a post-parser-unification project.

Related task:
We could either do this to the core Sanitizer code and have Parsoid reuse that component, or fix Parsoid's version and move that over to core or we could move sanitization to its own library .. whatever makes sense. But, one thing worth noting is that Parsoid does sanitization on tokens whereas core Sanitizer does sanitization on html. So, the unification is not entirely straightforward. It would require some refactoring to expose commonalities and leave the token or html specific wrappers in Parsoid and core.