> detects a violation of the required > > extended "prolog" (sorry, the HTML5 document declaration, which is not a > > valid "document declaration" for XHTML or for HTML4 or before or even for > > SGML, due to the unspecified schema after the shema short name), it > should > > catch this exception to try another parser. > > There is no spec, that I am aware of, that says that it should do that. >
But this is in the scope of the HTML5 whose claimed purpose is to become compatible with documents encoded in all previous flavors of HTML. Otherwise this claim is very weak and HTML5 is just a standard compatible with itself, and nothing else (it breaks XHTML rules, and SGML rules for the document declaration, and IETF charset naming rules with its reinterpretation of ISO8859-1, which is also still not stabilized). HTML5 is still beta in these claims, and it's regrettable that its required document declaration does not even specify its SGML catalog entry name, even if it forbids the insertion of a DTD. One day or another, at least the SGML catalog entry name will come back, when HTML5 will have been released and a newer version will be needed and developed, and HTML5 should still allow the presence of this SGML catalog entry name, even if it does not require it in this version.