The PHP protected keyword is an access modifier. It marks a property or method as protected. Protected properties and methods can only be used by the class in which the property or method was defined and any classes that derive from it. Any other code cannot use them.

<?php
class my_class {
    protected $number = 0;
}

class another_class extends my_class {
    public function add1() {
        $this -> number++;
    }

    public function getNumber() {
        return $this -> number;
    }
}

$obj = new another_class();
$obj -> add1();

echo 'The number is ' . $obj -> getNumber();
?>

The number is 1