# File lib/tree.rb, line 327
    def breadth_each &block
      node_queue = [self]       # Create a queue with self as the initial entry

      # Use a queue to do breadth traversal
      until node_queue.empty?
        node_to_traverse = node_queue.shift
        yield node_to_traverse
        # Enqueue the children from left to right.
        node_to_traverse.children { |child| node_queue.push child }
      end
    end