Discussion on the scope of the access modifiers private, protected, and public in php

Description: php's access modifiers private, protected, and public can only be used within the class.

2. protected can be used inside the class and in the inherited class. The class cannot be used outside [that is, the instantiated object cannot be called]

3. all public fields are applicable.

4. when the child class rewrites the methods in the parent class, the access modifier range in the child class must be greater than or equal to the parent class [inheritance can only be carried forward, at least unchanged. You cannot lose things .]