def to_xml_string(str ='')
str << <<SHAME_ON_YOU

<v:shape id="#{@id}" type="#_x0000_t202" fillcolor="#ffffa1 [80]" o:insetmode="auto"
  style="visibility:#{@visible ? 'visible' : 'hidden'}">
  <v:fill color2="#ffffa1 [80]"/>
  <v:shadow on="t" obscured="t"/>
  <v:path o:connecttype="none"/>
  <v:textbox style='mso-fit-text-with-word-wrap:t'>
   <div style='text-align:left'></div>
  </v:textbox>

  <x:ClientData ObjectType="Note">
   <x:MoveWithCells/>
   <x:SizeWithCells/>
   <x:Anchor>#{left_column}, #{left_offset}, #{top_row}, #{top_offset}, #{right_column}, #{right_offset}, #{bottom_row}, #{bottom_offset}</x:Anchor>
   <x:AutoFill>False</x:AutoFill>
   <x:Row>#{row}</x:Row>
   <x:Column>#{column}</x:Column>
   #{@visible ? '<x:Visible/>' : ''}
  </x:ClientData>
 </v:shape>
SHAME_ON_YOU

    end
serialize the shape to a string
@param [String] str
@return [String]