Stack discipline for actor base system

Q. How to traverse tree if processor receive data by querying XML storage one element at a time.
A. Reintroduce stack-discipline and use recursive algorithm as usually.

Stack need to store only variables  which `recursive algorithm would use. In case of XML traverse it is
tuple of (parentIndex, childName, childIndex) which defines any XML node uniquely.

foldActor () {
stack.pop(parentIndex, childName, childIndex) // restore stack

do stuff

push((parentIndex, childName, childIndex)) // push recurse step
}

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