each abstract method
Invokes the specified function
for node and each descendant in
breadth-first order,
such that a given node is only visited if all nodes of lesser depth have
already been visited, as well as all preceding nodes of the same depth.
The specified function is passed the current descendant, the zero-based
traversal index, and this node. If that
is specified, it is the this
context of the callback.
Implementation
@override
each(function, [that]);