Namespaces can be defaulted.

This applies to only element names without prefixes.

The syntax is: xmlns="some:uri"

Example:

<c:pseudocode xmlns:c="urn:publicid:IDN+mathdoc.org:pseudocode:en">

   <c:comment xmlns="http://www.w3.org/1999/xhtml">
     <p>This code does the following:</p>
     ...
   </c:comment>

</c:pseudocode>

You can undeclare the default: xmlns=""