The Node.lookupPrefix() method returns a DOMString containing the prefix for a given namespace URI, if present, and null if not. When multiple prefixes are possible, the result is implementation-dependent.
The Node.normalize() method puts the specified node and all of its sub-tree into a "normalized" form. In a normalized sub-tree, no text nodes in the sub-tree are empty and there are no adjacent text nodes.
The Node.setUserData() method allows a user to attach (or remove) data to an element, without needing to modify the DOM. Note that such data will not be preserved when imported via Node.importNode, as with Node.cloneNode() and Node.renameNode() operations (though Node.adoptNode does preserve the information), and equality tests in Node.isEqualNode() do not consider user data in making the assessment.