# File lib/rdoc/dot/dot.rb, line 243
        def to_s( t = '' )
            t + "#{@from} -> #{to} [\n" +
            @options.to_a.collect{ |i|
                i[1] && i[0] != 'label' ?
                    t + $tab + "#{i[0]} = #{i[1]}" :
                    i[1] ? t + $tab + "#{i[0]} = \"#{i[1]}\"" : nil
            }.compact.join( "\n" ) + "\n" + t + "]\n"
        end