type errorString … // New returns an error that formats as the given text. // // The returned error contains a Frame set to the caller's location and // implements Formatter to show this information when printed with details. func New(text string) error { … } func (e *errorString) Error() string { … } func (e *errorString) Format(s fmt.State, v rune) { … } func (e *errorString) FormatError(p Printer) (next error) { … }