[xml] Euro sign in xml:id

[Einhard Leichtfuß <alguien respiranto de>]

Hi,

I noticed that xmllint complains about the Euro sign ("€") in an xml:id.
 - "validity error : xml:id : attribute value € is not an NCName"

The W3C's XML specification, however, seems to allow this:
 - https://www.w3.org/TR/xml-id/#processing
 - https://www.w3.org/TR/xmlschema-2/#ID
 - https://www.w3.org/TR/xml-names/#NT-NCName
 - https://www.w3.org/TR/xml/#NT-NameStartChar
 * '€' is #x20ac which is in the range [#x2070-#x218F], a subset of
   NameStartChar, and may, therefore, occur anywhere in an NCName.

Am I mistaken above, should I look at another specification, or is this
a bug?

I am using version 2.9.10[+dfsg-6.7+deb11u1] on Debian bullseye.

Minimal example:
  <?xml version="1.0" encoding="UTF-8" ?>
  <x xml:id="€" />

Context: https://www.freelists.org/post/freedict/Ding-version-19

Regards,
Einhard