[STD31]    Internet Standard 31,
              <https://www.rfc-editor.org/info/std31>.
              At the time of writing, this STD comprises the following:

              Postel, J. and J. Reynolds, "Telnet Timing Mark Option",
              STD 31, RFC 860, DOI 10.17487/RFC0860, May 1983,
              <https://www.rfc-editor.org/info/rfc860>.