Package compfoo is a completion driver for Bonzai command trees and fulfills the bonzai.Completer package interface by returning "foo" and "bar". It is conventional to begin Completer packages with "comp" and always included a New function that returns a pointer to private struct that fulfills the bonzai.Completer interface. This is because multiple completions for different branch commands might use the same completion package but require different state. The Z.Comp, however, is the default used for any command that does not assign its own Cmd.Completer.