error

type Error interface {
	// Error implements error.
	Error() string

	// Has tests to see if the test error exists anywhere in the error
	// stack.
	Has(error) bool

	// Is tests to see if the test error matches most recent error in the
	// stack.
	Is(error) bool
}

type ErrorCaller interface {
	// Caller returns the associated Caller instance.
	Caller() std_caller.Caller
}

type ErrorWrapper interface {
	// WrapE returns the given error as a wrapper around the receiver.
	WrapE(error) error
}

type Unwrapper interface {
	// Unwrap returns the wrapped error, if any, otherwise nil.
	Unwrap() error
}

type Wrapper interface {
	// Wrap returns a new error defined by string that wraps the receiver.
	Wrap(string) error
}