def to_xml_string(str = '')
      str << '<xdr:twoCellAnchor>'
      str << '<xdr:from>'
      from.to_xml_string str
      str << '</xdr:from>'
      str << '<xdr:to>'
      to.to_xml_string str
      str << '</xdr:to>'
      object.to_xml_string(str)
      str << '<xdr:clientData/>'
      str << '</xdr:twoCellAnchor>'
    end
def to_xml_string(str = '')
      str << '<xdr:twoCellAnchor>'
      str << '<xdr:from>'
      from.to_xml_string str
      str << '</xdr:from>'
      str << '<xdr:to>'
      to.to_xml_string str
      str << '</xdr:to>'
      object.to_xml_string(str)
      str << '<xdr:clientData/>'
      str << '</xdr:twoCellAnchor>'
    end
Serializes the object
 @param [String] str
 @return [String]