# File lib/prawn/document/bounding_box.rb, line 136
    def canvas(&block)     
      init_bounding_box(block, :hold_position => true) do |_|
        @bounding_box = BoundingBox.new(self, [0,page_dimensions[3]], 
          :width => page_dimensions[2], 
          :height => page_dimensions[3] 
        ) 
      end
    end