The function set_attribute_node() does not work.  I have tried to retrieve an attribute from elsewhere in the document and then set the attribute in a new element node...and finding that perhaps I had to clone the node, I tried that as well with no luck.  Then I just tried to set_attribute_node() and passing it the result of create_attribute() and that didn't work.  So no test cases can show that this function actually adds an attribute_node to the tree.  Since append_child() is restricted for appending attributes, we are stuck with using only set_attribute().

Here is the test case:

$domelement->set_attribute_node($xml->create_attribute('foo', 'bar'));

result is that the tree is not affected.