[BCP222]   Best Current Practice 222,
              <https://www.rfc-editor.org/info/bcp222>.
              At the time of writing, this BCP comprises the following:

              Crocker, D., "Scoped Interpretation of DNS Resource
              Records through "Underscored" Naming of Attribute Leaves",
              BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019,
              <https://www.rfc-editor.org/info/rfc8552>.

              Crocker, D., "DNS Attrleaf Changes: Fixing Specifications
              That Use Underscored Node Names", BCP 222, RFC 8553,
              DOI 10.17487/RFC8553, March 2019,
              <https://www.rfc-editor.org/info/rfc8553>.