Aerys\StandardResponse::setReason PHP Method

    public function setReason(string $phrase) : Response
    {
        if ($this->state & self::STARTED) {
            throw new \LogicException("Cannot set reason phrase; output already started");
        }
        assert($this->isValidReasonPhrase($phrase), "Invalid reason phrase: {$phrase}");
        $this->headers[":reason"] = $phrase;
        return $this;
    }