The key is the stylesheet processing instruction (PI) in the second line.
关键是第二行中的样式表处理指令（PI）。
2
The second line is key, the stylesheet processing instruction (PI).
关键是第二行中的样式表处理指令(PI)。
3
The key idea here is that when the first instruction runs, all of the subsequent instructions in that block are guaranteed to be executed without interruption.