[BCP221]   Best Current Practice 221,
              <https://www.rfc-editor.org/info/bcp221>.
              At the time of writing, this BCP comprises the following:

              Hollenbeck, S. and A. Newton, "Registration Data Access
              Protocol (RDAP) Object Tagging", BCP 221, RFC 8521,
              DOI 10.17487/RFC8521, November 2018,
              <https://www.rfc-editor.org/info/rfc8521>.