def to_xml_string(str = '')
      str << '<?xml version="1.0" encoding="UTF-8"?>'
      str << ('<table xmlns="' << XML_NS << '" id="' << (index+1).to_s << '" name="' << @name << '" displayName="' << @name.gsub(/\s/,'_') << '" ')
      str << ('ref="' << @ref << '" totalsRowShown="0">')
      str << ('<autoFilter ref="' << @ref << '"/>')
      str << ('<tableColumns count="' << header_cells.length.to_s << '">')
      header_cells.each_with_index do |cell,index|
        str << ('<tableColumn id ="' << (index+1).to_s << '" name="' << cell.value << '"/>')
      end
      str << '</tableColumns>'
      table_style_info.to_xml_string(str)
      str << '</table>'
    end
def to_xml_string(str = '')
      str << '<?xml version="1.0" encoding="UTF-8"?>'
      str << ('<table xmlns="' << XML_NS << '" id="' << (index+1).to_s << '" name="' << @name << '" displayName="' << @name.gsub(/\s/,'_') << '" ')
      str << ('ref="' << @ref << '" totalsRowShown="0">')
      str << ('<autoFilter ref="' << @ref << '"/>')
      str << ('<tableColumns count="' << header_cells.length.to_s << '">')
      header_cells.each_with_index do |cell,index|
        str << ('<tableColumn id ="' << (index+1).to_s << '" name="' << cell.value << '"/>')
      end
      str << '</tableColumns>'
      table_style_info.to_xml_string(str)
      str << '</table>'
    end
Serializes the object
 @param [String] str
 @return [String]