[TYPO3-english] Re: Looking for Tutorial for own compatibility extension

[anybody]

[Additional remark]

I moved formally from XHTML+RDFa to XHTML5 (with backward compatibility to XHTML+RDFa 1.0, I am against - often short living - hypes) because of some problems with extensions using tags or attributes of HTML5 which made problems with the DTD. So I needed pages with another doctype for mailforms und search forms and got a mixed doctype site - an option I would like to avoid in the future.
Also Typo3 was never supporting the actual standard of XHTML+RDFa 1.1 (there is only an option for v1.0).
To use HTML5 (SGML) would produce a "Kauderwelsch" of XML methods inside a SGML based standard. The most browsers would accept it, but it would be like the HTML practised in the early 90ies.