Is there a tool that transforms (or filters losing spurious information) "any HTML5" into Polyglot XHTML5?
Preferably a tool based on extensions for DOM (or XSLT or XQuery).
The validator.nu is the most reliable tool for validation... Perhaps some filters can be developed from
validator.nuinfrastructure. Some old (2011's) XSLTs, like polyglototron.sch and polyglot-xhtml5.xsd, was developed as open source, but no enhances or updates was noticed.