For a global declaration, you need to specify its type (that is, class name) and the identifier you want to use to refer to it (that is, variable name).
对于global声明，需要指定它的类型(即类名)和想要用于引用它的标识符(即变量名)。
2
The variable name can be any normal identifier, like x.
其中的变量名可以是任何一般的标识符，如x。
3
Here the self identifier declares a thread local variable time.