protected function mixedKeyword(&$out)
    {
        $parts = [];

        $oldWhite = $this->eatWhiteDefault;
        $this->eatWhiteDefault = false;

        for (;;) {
            if ($this->keyword($key)) {
                $parts[] = $key;
                continue;
            }

            if ($this->interpolation($inter)) {
                $parts[] = $inter;
                continue;
            }

            break;
        }

        $this->eatWhiteDefault = $oldWhite;

        if (!$parts) {
            return false;
        }

        if ($this->eatWhiteDefault) {
            $this->whitespace();
        }

        $out = $parts;

        return true;
    }