Picture one piece of paper with two boxes on it. The signature box is filled in. The amount box is empty. Whoever holds that paper decides what goes in the empty box, and the person who signed has already agreed to it. Everything this entry teaches comes out of that one uncomfortable moment of handing it over.
可以想成一張紙，上面有兩個欄位。簽名欄已經填好了。金額欄是空的。拿著這張紙的人決定空欄要填多少，而簽名的人事先就同意了。這個條目要教的兩個用法，都是從「把這張紙交出去」的那一刻長出來的。
登入就可以看每一支怎麼連回核心畫面。