The namespace URI of this node, or null if it is unspecified.
This is not a computed value that is the result of a namespace lookup based
on an examination of the namespace declarations in scope. It is merely the
namespace URI given at creation time.
For nodes of any type other than ELEMENT and ATTRIBUTE and nodes created
with a DOM Level 1 method, such as Document.createElement, this is always null.
The namespace URI of this node, or null if it is unspecified. This is not a computed value that is the result of a namespace lookup based on an examination of the namespace declarations in scope. It is merely the namespace URI given at creation time. For nodes of any type other than ELEMENT and ATTRIBUTE and nodes created with a DOM Level 1 method, such as Document.createElement, this is always null.