When using prefixes in XML, a so-called namespace for the prefix must be defined.

The namespace is defined by the xmlns attribute in the start tag of an element.

The namespace declaration has the following syntax. xmlns:prefix="URI".

<root>

<h:table xmlns:h="http://www.w3.org/TR/html4/">
  <h:tr>
    <h:td>Apples</h:td>
    <h:td>Bananas</h:td>
  </h:tr>
</h:table>

</root>

In the example above, the xmlns attribute in the tag give the h: prefixe a qualified namespace.