If there is already a namespace declaration with the same uri in the root-node of the document, the prefix of this is taken, otherwise it will take the one provided in the optional parameter prefix or generate a random one.
This function returns a new instance of class DomElement. The tag name of the element is the value of the passed parameter name. The URI of the namespace is the value of the passed parameter uri. If there is already a namespace declaration with the same uri in the root-node of the document, the prefix of this is taken, otherwise it will take the one provided in the optional parameter prefix or generate a random one. This node will not show up in the document unless it is inserted with e.g. domnode_append_child().