what is the exact usage of xmlns in xml, and html

Question

Does any one know what is the exact usage of xmlns in HTML, XML files?

Edit: Why do we need this namespace? What is its usage?

Answer 1

The xmlns attribute declares an XML Namespace. The Namespaces in XML standard discusses this element in depth.

Namespaces are used primarily to avoid conflicts between element names when mixing XML languages. If you have a particular application that you have questions about, perhaps you could post an example.