Error codes appearing in the DNS header and in these three RR types all refer to the same error code space with the single exception of error code 16 which has a different meaning in the OPT RR from its meaning in other contexts. See table below. 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.
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. 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. At the present time, there are two categories of label types, data labels and compression labels.