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Zones are a mechanism to support structured addressing of ACP addresses within the same /48 ULA prefix. ¶ The key words " MUST ", " MUST NOT ", " REQUIRED ", " SHALL ", " SHALL NOT ", " SHOULD ", " SHOULD NOT ", " RECOMMENDED ", " NOT RECOMMENDED ",
" MAY ", and " OPTIONAL " in this document are to be interpreted as
described in BCP 14 [ RFC2119 ] [ RFC8174 ] when, and only when, they appear in all capitals, as shown here. ¶ 3.