The use of namespaces is not limited to elements--you can apply them
to attributes as well. Here is an example:

<orderReport xmlns:order="http://myserver.com/orders"
      xmlns:catalog="http://myserver.com/catalog">

 <item order:orderId="1234" catalog:itemNumber="456" />
 <item order:orderId="5678" catalog:itemNumber="789" />

</rootElement>

As with element names, this allows you to pull attributes from
multiple sources into a single document.