t represents the edge from a child incremental to a parent expert node. A
t is stateful, you cannot use the same
t to link one child node to multiple parents at the same time.
create ?on_change child, nothing happens until the
t is linked to a parent. see
Node.add_dependency for documentation of
val value : 'a t -> 'a
value t reads the value of the child incremental. It can only be used from the callback of the
Expert.Node.t that has
t in its set of dependencies.