Eastlake, et al. See section 3.1. See section 3.2. Zero is interpreted to mean that the RR can only be used for the transaction in progress. Eastlake, et al.
Data TYPEs are the primary means of storing data.
Meta-TYPEs designate transient data associated with an particular DNS message and in some cases can also be used in queries. Eastlake, et al. 0x0000 - assignment requires an IETF Standards Action. 65535 0xFFFF - can only be assigned by an IETF Standards Action. By definition, the null or ROOT label can not be used for any other NAME purpose.