The classification of an abstract identifier as a certificate identifier must be inherent to the FDL (perhaps thought of as a table of certificate identifiers supported by the FDL), as is its further classification as indicating normal certificates as opposed to indicating
A certificate identifier may be thought of as identifying the method of executing certificate creation and reconsideration code. These are created by the FDL implementors. A certificate kind pairs a certificate identifier with an object containing creation and reconsideration code. Such certificate code would typically be created by users. If FDL implementors determine that improvements must be made to how certificate code is executed, a new certificate identifier must be added while the old certificate identifier must continue to have its old interpretation. Pairing old certificate code objects with new certificate identifiers gives new certificate kinds.
Certificate identifiers for borrowed certificates must be bound by the FDL to a