[BCP43]    Best Current Practice 43,
              <https://www.rfc-editor.org/info/bcp43>.
              At the time of writing, this BCP comprises the following:

              Droms, R., "Procedures and IANA Guidelines for Definition
              of New DHCP Options and Message Types", BCP 43, RFC 2939,
              DOI 10.17487/RFC2939, September 2000,
              <https://www.rfc-editor.org/info/rfc2939>.