def write_xml(options = { mapping: :_default })
      xml = save_to_xml(options)
      formatter = REXML::Formatters::Pretty.new
      formatter.compact = true
      io = ::StringIO.new
      formatter.write(xml, io)
      io.string
    end
def write_xml(options = { mapping: :_default })
      xml = save_to_xml(options)
      formatter = REXML::Formatters::Pretty.new
      formatter.compact = true
      io = ::StringIO.new
      formatter.write(xml, io)
      io.string
    end
Writes this mapped object as a pretty-printed XML string.

 @param options [Hash] the options to be passed to
   [XML::Mapping#save_to_xml](http://multi-io.github.io/xml-mapping/XML/Mapping.html#method-i-save_to_xml)
 @return [String] the XML form of the object, as a compact, pretty-printed string.