This distinguishes whether a related security notification concerns a Certificate Authority (CA) object or a Certificate Revocation List (CRL) object. Since CA and CRL problems require different remediation, installing or updating a trusted CA cert versus refreshing a revocation list that may have gone stale, an admin's response to a CA-CRL-related alarm depends entirely on correctly reading this field before deciding what to actually go fix. For example, a notification with this set to CRL alongside the invalid-CA-reason object populated would point the admin at refreshing an expired or unreachable CRL rather than at the CA certificate itself.