How to add comment in XML sitemap

Question

I want to add comment tag in my manually generated XML sitemap to grouping urls like this:

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <!-- Book -->
  <url>
    <loc>http://example.com/Book</loc>
  </url>
  <!-- Notebook -->
  <url>
    <loc>http://example.com/Notebook</loc>
  </url>
  <!-- Pen -->
  <url>
    <loc>http://example.com/Pen</loc>
  </url>
</urlset>

Is it possible?

Answer 1

That should be fine, in the sitemap protocol there is an example with a comment like the ones you used: http://www.sitemaps.org/protocol.html#extending

<!-- my comment -->