定方向：求「下一个」→ 倒序；求「上一个」→ 正序。
The primary signal is desiredSize on the controller. It can be positive (wants data), zero (at capacity), negative (over capacity), or null (closed). Producers are supposed to check this value and stop enqueueing when it's not positive. But there's nothing enforcing this: controller.enqueue() always succeeds, even when desiredSize is deeply negative.
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圖像加註文字，以日本動畫風格描繪的小屋場景中，伊利亞與謝恩同框出現。青少年時期踏入這個世界，對王艾青博士來說，有一種吸引人的「酷」感。她現為利物浦大學（University of Liverpool）中文系高級講師，她形容那種體驗就像加入一個秘密社群。