Errors in RFC 2307 and nis.schema?

["Chuck Coker" <chuckc@tyrell.com>]

In RFC 2307 and the nis.schema file that ships with OpenLDAP, the following
two entries list "description" as both MUST and MAY. Is there a reason for
this? Doesn't the MUST clause override the MAY clause, i.e., since it is in
the MUST clause, doesn't that make it a required attribute?

( nisSchema.2.4 NAME 'ipProtocol' SUP top STRUCTURAL
    DESC 'Abstraction of an IP protocol. Maps a protocol number
        to one or more names. The distinguished value of the cn
        attribute denotes the protocol's canonical name'
    MUST ( cn $ ipProtocolNumber $ description )
    MAY description )

( nisSchema.2.5 NAME 'oncRpc' SUP top STRUCTURAL
    DESC 'Abstraction of an Open Network Computing (ONC)
        [RFC1057] Remote Procedure Call (RPC) binding.
        This class maps an ONC RPC number to a name.
        The distinguished value of the cn attribute denotes
        the RPC service's canonical name'
    MUST ( cn $ oncRpcNumber $ description )
    MAY description )

----------------------------------------------------------------------
Chuck Coker <chuckc@tyrell.com>
Software Developer, Tyrell Software Corporation
23151 Verdugo Drive, Suite 204
Laguna Hills, California 92653 United States
+1 949 458 1911 ext. 3