RegisterExceptionType

RegisterExceptionType[sym]
RegisterExceptionType[sym, parent]
RegisterExceptionType[sym, {parent1, parent2, ...}]

registers sym as a symbolic exception type, optionally declaring one or more parent exception types.

Example

RegisterExceptionType[FileReadError, "IOError"];

ExceptionTypeRegisteredQ[FileReadError]
ExceptionTypes["IOError"]

Registration clears prior definitions on sym and protects it. Register only symbols intended to serve as exception types.

See the official Wolfram Language reference for registration and deregistration details.