pkg flag, type FlagSet struct, Usage func()
pkg flag, type Value interface { Set, String }
pkg flag, type Value interface, Set(string) error
pkg flag, type Value interface, String() string
pkg flag, var ErrHelp error
pkg flag, var Usage func()
pkg fmt, func Errorf(string, ...interface{}) error
pkg fmt, func Fprint(io.Writer, ...interface{}) (int, error)
pkg fmt, func Fprintf(io.Writer, string, ...interface{}) (int, error)