[jayd16]

It's good practice to throw an exception from your own namespace if you're writing a library.

You don't want to expose an implementation detail like some specific exception as part of your public API and have to worry about breaking that later.

You could overload some built in exception but IMO that's not the best practice. You muddy your API and a caller has to wrap your exception if they want to bubble it up and catch it specifically, anyway.