TElPGPRevocableSignatureSubpacket is a descendant of TElPGPSignatureSubpacket class.
The following paragraph is taken from RFC 2440 - OpenPGP messages format, part 18.104.22.168.:
«Signature's revocability status. Packet body contains a boolean flag indicating whether the signature is revocable. Signatures that are not revocable have any later revocation signatures ignored. They represent a commitment by the signer that he cannot revoke his signature for the life of his key.»