A member of a Scala.Rx dataflow graph. Apart from the fact that it has a name
and a current level in the graph, we don't really know much about it. It could
be either a Emitter or a Reactor or both.
A number giving an approximate ordering of the current Node in the
dataflow graph it is part of.
Vars have it set to 0 and Obs have it set to Long.MaxValue because
they're always the root and leaves of the graph. For other Rxs it
depends on their location within the dataflow graph, and can change over
time if the shape of the graph is changing.
The name of this object, generally passed in as a String when it is
This can be inspected later, and is handy for debugging and logging