Colon is ignored when using "xhtml:link" in the XML Node sitemap.

I'm working on a multilingual site, and when I try to add the "xhtml:link" with the XML node, the colon gets ignored. I tried different string concatenation solutions, but none worked. I have the same issue with comments "<!-- -- >".

Is it a bug? Is there any solution to add a tag with a colon with the XML node?

I found in the documentation that Webstudio creates robots.txt, but it doesn't specify how to create or edit it. Is there currently a way of doing it?