# File lib/edi4r/diagrams.rb, line 533
    def down!
      this_node = self.node
      return nil if (tail=this_node.tail).nil?
      # Save current co-ordinates on stack
      @coord_stack.push( @coord )
      # Init. co-ordinates for the new level:
      @coord = NodeCoords.new(tail, 0, 0)
      self
    end