def METHOD_NAME(self, node_name, macs):
    """Register an invocation of a registered operation node and store the
    specified number of MAC's. Nodes may be invoked multiple times.
    Invocations are stored in order."""
    node = self._nodes_by_name[node_name]
    node['uses'] += 1
    node['macs'] += macs  # we accumulate mac's across multiple invocations
    self._invocations.append(node_name)