If the node passed has children itself, they will be duplicated as well, which makes it quite easy to duplicate large parts of a xml document.
Before a new sibling is added it is first duplicated. Therefore the new child is a completely new copy which can be modified without changing the node which was passed to this function. If the node passed has children itself, they will be duplicated as well, which makes it quite easy to duplicate large parts of a xml document. The return value is the added sibling. If you plan to do further modifications on the added sibling you must use the returned node.