def to_xml_string(str = '')
      str << '<xf '
      serialized_attributes str
      str << '>'
      alignment.to_xml_string(str) if self.alignment
      protection.to_xml_string(str) if self.protection
      str << '</xf>'
    end
def to_xml_string(str = '')
      str << '<xf '
      serialized_attributes str
      str << '>'
      alignment.to_xml_string(str) if self.alignment
      protection.to_xml_string(str) if self.protection
      str << '</xf>'
    end
Serializes the object
 @param [String] str
 @return [String]