doc.elements.each('Drawing/box') do |box_element|
self << Box.new(box_element)
end
doc.elements.each('Drawing/link') do |link_element|
self << Link.new(link_element, self.vertices)
end
doc.elements.each('Drawing/box') do |box_element|
self << Box.new(box_element)
end
doc.elements.each('Drawing/link') do |link_element|
self << Link.new(link_element, self.vertices)
end