Replaces the child node oldChild with newChild in the list of children,
and returns the oldChild node.
If newChild is a DocumentFragment object, oldChild is replaced by
all of the DocumentFragment children, which are inserted in the same
order. If the newChild is already in the tree, it is first removed.
Replaces the child node oldChild with newChild in the list of children, and returns the oldChild node. If newChild is a DocumentFragment object, oldChild is replaced by all of the DocumentFragment children, which are inserted in the same order. If the newChild is already in the tree, it is first removed.