[STD67]    Internet Standard 67,
              <https://www.rfc-editor.org/info/std67>.
              At the time of writing, this STD comprises the following:

              Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
              2006, <https://www.rfc-editor.org/info/rfc4506>.