I want to check if an HTML5 document follows the polyglot markup profile as defined by http://www.w3.org/TR/html-polyglot/. AFAIK first validating as HTML and then as XML doesn’t suffice for this.
Input of the HTML5 document as URL, file upload and/or text input.
It can be anything (a Web app, a library, a desktop client for any OS, …), as long as it is FLOSS.
What I tried/know
According to its website, Total Validator supports it ("3rd August 2014 - Total Validator v8.5.0 released: Polyglot Markup updated to 17 July 2014"). They offer a FLOSS Firefox extension, however, you seem to have to install their proprietary client in addition to make it work.