You can put a variable there, and because it's not encapsulated in curly braces, as we just discussed, that essentially means it's accessible everywhere in that file.

你可以加入一个变量，因为它不是封装在花括号里，就像我们刚才讨论的，本质的意思是它可以在文件的所有地方,都可以被访问到。

哈佛公开课 - 计算机科学课程节选