Explain visibility modifiers in PHP classes.

public: Accessible from anywhere\nprivate: Only accessible within the same class\nprotected: Accessible within the class and its subclasses\n\nExample:\nclass MyClass {\n public $publicVar = "Everyone can see this";\n private $privateVar = "Only MyClass can see this";\n protected $protectedVar = "MyClass and subclasses can see this";\n}\n\nclass ChildClass extends MyClass {\n public function test() {\n echo $this->publicVar; // OK\n echo $this->protectedVar; // OK\n echo $this->privateVar; // Error!\n }\n}