Service Pack 2 for 11.2 adds html5 support to Tidy.
From the release notes:
"2.1.21 New Tidy version supports HTML5
A new tidy version is available in addition to the existing tidy options. The tidy options HTML, HTML5 (tidy 4.9.15), XHTML, XHTML (tidy 4.9.15), XML, or XML (tidy 4.9.15) are available for compliance check and corrections. Tidy version 4.9.15 has been integrated to support HTML5. Note that Tidy version 4.9.15 is not officially released by the HTML Tidy Advocacy Community Group (HTACG)."