private static function process_keyframe_interval($keyframe_interval)
    {
        if (is_string($keyframe_interval) || $keyframe_interval == null) {
            return $keyframe_interval;
        }
        if (!is_numeric($keyframe_interval)) {
            throw new InvalidArgumentException("Keyframe interval should be a number or a string");
        }
        if ($keyframe_interval < 0) {
            throw new InvalidArgumentException("Keyframe interval should be greater than zero");
        }
        if (is_int($keyframe_interval)) {
            return $keyframe_interval . ".0";
        }
        return $keyframe_interval;
    }