'Replace from start to stop child index of parent with t, which might
be a list.  Number of children may be different
after this call.  The stream is notified because it is walking the
tree and might need to know you are monkeying with the underlying
tree.  Also, it might be able to modify the node stream to avoid
restreaming for future phases.
If parent is null, don\'t do anything; must be at root of overall tree.
Can\'t replace whatever points to the parent externally.  Do nothing.'

def replaceChildren(self, parent, startChildIndex, stopChildIndex, t):

    raise NotImplementedError
