Man Page XML (refentry, refsection): xi::include doesn't work for me

I would like to include some DB coded xml into an xml source file (DB
5 with namespaces) for a man page but I keep getting validation errors
(using xmllint --schema).  Is it possible as it is in other parts like
chapter, article, etc.?

Here's a fragment showing how I'm trying to use it:

<refentry
  xmlns="http://docbook.org/ns/docbook"
  xmlns:xi="http://www.w3.org/2001/XInclude"
  version="5.0" xml:id="attributes"
>
<!-- ... -->
<refsection>
  <para>
  <xi:include href="./attributes-standard-table.xml" parse="xml"/>
  </para>
</refsection>
<!-- ... -->
</refentry>

Note that if the code in the external file (a <table>) is included
manually the file validates fine.

Thanks for any help.

Best regards,

-Tom