In PHP, there are three main visibility modifiers that are used to control access to class properties and methods:
`public`: Class members (properties and methods) defined as public can be accessed from anywhere, even outside the class.
`protected`: Class members defined as protected can only be accessed within the class that defines them, and in their subclasses.
`private`: Class members defined as private can only be accessed within the class itself that defines them.
These modifiers help to control the level of access to class properties and methods in PHP, providing a starting point for implementing encapsulation and restricting access to some parts of the class.
