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I validated a XHTML 1.1 document. The html tag was a plain tag which looked like this; <html> But as far as I know, the standard does require the xmlns attribute. Yet the validator validates the document as correct XHTML 1.1 even though the mandatory xmlns attribute was not present. In my browser my document didnt work until I changed it to ths; <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
The spec indeed requires a strictly conforming document to have the xmlns attribute for the html element http://www.w3.org/TR/xhtml11/conformance.html#strict However, it looks like the DTD (the grammar published with the standard, and used to validate) does not include any such requirement. I'll ask the spec authors whether this was a mistake or if the omission in the DTD was on purpose.
As checked with the HTML working group, the presence of the xmlns attribute for the html element is something that they had in the conformance criteria, but could not enforce through the DTD. This is not as such an issue of validation, but should be considered as an extra check as we make the validator evolve toward being a conformance checker. tagged notInDTD
*** This bug has been marked as a duplicate of bug 68 ***
In XHTML 1.1, the XHTML namespace is required to be the fixed value "http://www.w3.org/1999/xhtml", but it is also allowed to expand the namespace: <html xmlns="http://www.w3.org/1999/xhtml" xmlns:wairole= "http://www.w3.org/2005/01/wai-rdf/ GUIRoleTaxonomy#" xmlns:x2="http://www.w3.org/2002/06/xhtml2" xmlns:aaa="http://www.w3.org/2005/07/aaa"> In http://www.w3.org/TR/xhtml-modularization/DTD/xhtml-qname-1.mod the xmlns attribute is set to #FIXED with the value "http://www.w3.org/1999/xhtml": <!ENTITY % XHTML.xmlns.attrib.prefixed "xmlns:%XHTML.prefix; %URI.datatype; #FIXED '%XHTML.xmlns;'" > But it is allowed to extend the namespaces via %XHTML.xmlns.extra.attrib - that's the "X" in "XHTML".