func Errorf(format string, a ...interface{}) error {
	e := fmt.Errorf(format, a...)
	ee := Error{}
	ee.msg = e.Error()
	ee.cause = errors.Unwrap(e)
	return ee
}

// Unwrap the internal error.
func (e Error) Unwrap() error { return e.cause }

// Error 'error' compatible method.
func (e Error) Error() string {
	if e.msg == "" {
		return "crypto: cause <nil>"
	}
	return e.msg
}

// the string as a value that satisfies error of type tagging.Error
func Errorf(format string, a ...interface{}) error {
	return Error{err: fmt.Errorf(format, a...)}
}

// Unwrap the internal error.
func (e Error) Unwrap() error { return e.err }

// Error 'error' compatible method.
func (e Error) Error() string {
	if e.err == nil {
		return "replication: cause <nil>"
	}
	return e.err.Error()

// the string as a value that satisfies error of type tagging.Error
func Errorf(format string, a ...interface{}) error {
	return Error{err: fmt.Errorf(format, a...)}
}

// Unwrap the internal error.
func (e Error) Unwrap() error { return e.err }

// Error 'error' compatible method.
func (e Error) Error() string {
	if e.err == nil {
		return "versioning: cause <nil>"
	}
	return e.err.Error()

// the string as a value that satisfies error of type tagging.Error
func Errorf(format string, a ...interface{}) error {
	return Error{err: fmt.Errorf(format, a...)}
}

// Unwrap the internal error.
func (e Error) Unwrap() error { return e.err }

// Error 'error' compatible method.
func (e Error) Error() string {
	if e.err == nil {
		return "lifecycle: cause <nil>"
	}
	return e.err.Error()

type PartialAddError struct {
	inner error
}

func (e *PartialAddError) Error() string {
	return fmt.Sprintf("%s: %v", ErrPartialAdd.Error(), e.inner)
}

func (e *PartialAddError) Unwrap() []error {
	return []error{ErrPartialAdd, e.inner}
}

func NewErrPartialAdd(err error) *PartialAddError {
	return &PartialAddError{
		inner: err,
	}