1: Declaration of namespace, which must be on the first line of the page
2: After the namespace declaration, subsequent classes and functions are blocked in the namespace
3: require/include other pages with namespaces, their own space is not disturbed
4: If you want to explicitly use a class in a certain space, you can gradually search from the root space, such as \zixueit\Class()
5: If you frequently use a class in a certain space, you can use the declaration first
6: Parameters of the auto-loading function, including "space path\class name"