The architect asked for external functions, which I didn’t know the precise answer to. After the call finished up, I did some googling and the closest approximation to what he was asking about may have been regarding a Swift function’s external parameters. External parameters can be used in a function to describe what parameters being passed into a Swift function can be used for. Instead of func join(s1: String, s2: String) External parameters describe things much more concisely: func join(fromString s1: String, toString s2: String)