Google sitemap namespace confusion

Question

Here the structure of my sitemap:

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
    <sitemap>
        <loc>somefile.xml</loc>
    </sitemap>
</sitemapindex>

somefile.xml

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.google.com/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">
<url>
  <loc>[some url]</loc>
  <link rel="alternate" hreflang="en" href="[some url]" />
  <link rel="alternate" hreflang="en" href="[some url]?lang=en" />
  <link rel="alternate" hreflang="fr" href="[some url]?lang=fr" />
  <priority>1.00</priority>
</url>

Here is Google's error message:

Your Sitemap or Sitemap index file doesn't properly declare the namespace. Expected: http://www.sitemaps.org/schemas/sitemap/0.9 Found: http://www.w3.org/1999/xhtml Tag: urlset

I guess I'm missing something, information on the Internet are confusing. What's is the right syntax? Thank you if you can help.

Answer 1

Problem solved by replace add the xhtml namespace to all the 'link' tags.

Replacing

<link

with

<xhtml:link 

Answer 2

You should add xmlns="http://www.w3.org/1999/xhtml" to your URL:

<link rel="alternate" hreflang="en" href="[some url]" xmlns="http://www.w3.org/1999/xhtml" />