sitemap.xml template used with alternates for multiple languages returns an invalid xml

[Viggie]

The generated xml has following validation error: "Error 1845: Element '{​http://www.w3.org/1999/xhtml}link': No matching global element declaration available, but demanded by the strict wildcard."

This ​response in StackOverflow contains the correct fix.

The error in the sitemap.xml template error is simply a missing slash for xmlns:xhtml="http://www.w3.org/1999/xhtml/" ​in line 2.

[Mariusz Felisiak]

"​http://www.w3.org/1999/xhtml/" without a trailing slash should be completely valid. Florian, Can you take a look?

[Florian Demmer]

What validator was used to produce this error?

Not only is the namespace name "​http://www.w3.org/1999/xhtml" valid, the name "​http://www.w3.org/1999/xhtml/" (with trailing slash) would be a different namespace.

As specified in ​2.3 Comparing URI References:

URI references identifying namespaces are compared when determining whether a name belongs to a given namespace, and whether two names belong to the same namespace. [Definition: The two URIs are treated as strings, and they are identical if and only if the strings are identical, that is, if they are the same sequence of characters. ] The comparison is case-sensitive, and no %-escaping is done or undone.

and ​3 Declaring Namespaces:

The namespace name, to serve its intended purpose, SHOULD have the characteristics of uniqueness and persistence. It is not a goal that it be directly usable for retrieval of a schema (if any exists).

The namespace name for XHTML is specified ​here:

The namespace name ​http://www.w3.org/1999/xhtml is intended for use in various specifications such as: [...]

Therefore I conclude, that the validator and the StackOverflow recommendations are wrong and nothing should be changed in the sitemap.xml template.

[Mariusz Felisiak]

Florian, thanks for checking!