code: func Errorf(l *State, format string, a ...interface{}) {
  	Where(l, 1)
  	l.PushFString(format, a...)
  	l.Concat(2)
  	l.Error()
  }
docs: // Errorf raises an error. The error message format is given by format plus
  // any extra arguments, following the same rules as PushFString. It also adds
  // at the beginning of the message the file name and the line number where
  // the error occurred, if this information is available.
  //
  // This function never returns. It is an idiom to use it in Go functions as:
  //   lua.Errorf(l, args)
  //   panic("unreachable")