    # File lib/prawn/text.rb, line 27
        def height_of(string, options={})
          process_final_gap_option(options)
          box = Text::Box.new(string,
                              options.merge(:height   => 100000000,
                                            :document => self))
          box.render(:dry_run => true)
          height = box.height - box.descender
          height += box.line_height + box.leading - box.ascender if @final_gap
          height
        end