func (pe *ProtocolError) Is(err error) bool {
	return pe == ErrNotSupported && err == errors.ErrUnsupported
}

var (
	// ErrNotSupported indicates that a feature is not supported.
	//
	// It is returned by ResponseController methods to indicate that
	// the handler does not support the method, and by the Push method
	// of Pusher implementations to indicate that HTTP/2 Push support
	// is not available.