I've written an API which can be configured to signal errors in different ways (return values, debugging messages, or exceptions). I've got a check in place when the API is first initialized to see what type of error handling the client is requesting - what should I do when they request an undefined error handling type?
This is kind of similar to "Where do I log the error that I can't write to the logfile?"
Do I go with the idiom of the language, do I fatal? Do I throw an exception, even though if they aren't asking for exception handling they probably haven't wrapped the call in a try/catch? The language I'm writing doesn't have an ENUM type so it can't be a type error.