Class Constants Visibility

Class constant may have a visibility option. This limits their accessibility to the current class, its class hierarchy or any other class. Visibilities for class constants are : private, protected and public.

<?php

class x {
     // This class can only be used in x
    private const C1 = 1;

     // This class can only be used in x and y
    protected const C2 = 1;

     // This class can be used in x, y and z
    private const C3 = 1;
}

class y extends x {
     // doSomething()
}

class z {
     // doSomething()
}

?>

Documentation

Related : Visibility

Added in PHP 7.1