[BCP89]    Best Current Practice 89,
              <https://www.rfc-editor.org/info/bcp89>.
              At the time of writing, this BCP comprises the following:

              Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, DOI 10.17487/RFC3819, July 2004,
              <https://www.rfc-editor.org/info/rfc3819>.

              Briscoe, B. and J. Kaippallimalil, "Guidelines for Adding
              Congestion Notification to Protocols that Encapsulate IP",
              BCP 89, RFC 9599, DOI 10.17487/RFC9599, August 2024,
              <https://www.rfc-editor.org/info/rfc9599>.