go/src/fmt/errors.go

// Errorf formats according to a format specifier and returns the string as a
// value that satisfies error.
//
// If the format specifier includes a %w verb with an error operand,
// the returned error will implement an Unwrap method returning the operand.
// If there is more than one %w verb, the returned error will implement an
// Unwrap method returning a []error containing all the %w operands in the
// order they appear in the arguments.
// It is invalid to supply the %w verb with an operand that does not implement
// the error interface. The %w verb is otherwise a synonym for %v.
func Errorf(format string, a ...any) error { … }

type wrapError …

func (e *wrapError) Error() string { … }

func (e *wrapError) Unwrap() error { … }

type wrapErrors …

func (e *wrapErrors) Error() string { … }

func (e *wrapErrors) Unwrap() []error { … }