This function replaces the child oldnode with the passed new node
public function replaceChild<T as DOMNode>( DOMNode $newchildobj, DOMNode $oldchildobj, ): T;
If the new node is already a child it will not be added a second time. If the replacement succeeds the old node is returned.
DOMNode $newchildobj- The new node. It must be a member of the target document, i.e. created by one of the DOMDocument->createXXX() methods or imported in the document by DOMDocument::importNode.
DOMNode $oldchildobj- The old node.
mixed- - The old node or FALSE if an error occur.