[BCP118]   Best Current Practice 118,
              <https://www.rfc-editor.org/info/bcp118>.
              At the time of writing, this BCP comprises the following:

              Zeilenga, K., "Considerations for Lightweight Directory
              Access Protocol (LDAP) Extensions", BCP 118, RFC 4521,
              DOI 10.17487/RFC4521, June 2006,
              <https://www.rfc-editor.org/info/rfc4521>.