What types of access restrictions to properties and methods in PHP do you know?

In PHP, there are three main levels of access to class properties and methods:

• public — access is open everywhere, from any part of the code.
• protected — access is allowed within the class itself and its descendants.
• private — access is only allowed within the class itself; even descendants cannot access it.

Example:

class Example {
    public $publicProp = 'public';
    protected $protectedProp = 'protected';
    private $privateProp = 'private';

    public function showProps() {
        echo $this->publicProp . "\n";
        echo $this->protectedProp . "\n";
        echo $this->privateProp . "\n";
    }
}

class ChildExample extends Example {
    public function showProtected() {
        echo $this->protectedProp; // Access is allowed
        // echo $this->privateProp; // Error, private is not accessible
    }
}

$obj = new Example();
$obj->showProps();
// echo $obj->protectedProp; // Error
// echo $obj->privateProp; // Error

These restrictions help encapsulate data and control access to the internal state of objects.