XML Default Namespace
The namespaces we created in the previous two lessons involved applying a prefix. We applied the prefix when we defined the namespace, and we applied a prefix to each element that referred to the namespace.
You can also use what is known as a default namespace within your XML documents. The only difference between a default namespace and the namespaces we covered in the previous two lessons is, a default namespace is one where you don't apply a prefix.
You can also define namespaces against a child node. This way, you could use multiple namespaces within the same document if required.
Example Default Namespace
Here, we define the namespace without a prefix:
<books xmlns="http://somebooksite.com/book_spec">
<book>
<title>The Dream Saga</title>
<author>Matthew Mason</author>
</book>
...
</books>
When you define the namespace without a prefix, all descendant elements are assumed to belong to that namespace, unless specified otherwise (i.e. with a local namespace).
Real Life Example
When writing XHTML documents, authors usually define http://www.w3.org/1999/xhtml as the default namespace. Doing this enables authors to use the XHTML tags without a prefix.