[BCP154]   Best Current Practice 154,
              <https://www.rfc-editor.org/info/bcp154>.
              At the time of writing, this BCP comprises the following:

              Wolf, K. and A. Mayrhofer, "Considerations for Civic
              Addresses in the Presence Information Data Format Location
              Object (PIDF-LO): Guidelines and IANA Registry
              Definition", BCP 154, RFC 5774, DOI 10.17487/RFC5774,
              March 2010, <https://www.rfc-editor.org/info/rfc5774>.