public int getRecursionLevel() {
        return dataListListenerStack.size() - 1;
    }
How deep into the tree of nested data lists the callback currently is.
beginList() is invoked after this is increased, and endList() is
invoked before it is decreased.

@return an integer of 1 or above
container-core/src/main/java/com/yahoo/processing/rendering/AsynchronousSectionedRenderer.java