xmlns refers to the XML namespace
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".
Note: The namespace URI is not used by the parser to look up information.
The purpose is to give the namespace a unique name. However, often companies use the namespace as a pointer to a web page containing namespace information.