PHP define constant in class and use constant

https://www.php.net/manual/en/language.oop5.constants.php 

<?php

const ONE = 1;
class foo {    // Auto public
    const TWO = ONE * 2;
    const THREE = ONE + self::TWO;
    const SENTENCE = 'The value of THREE is '.self::THREE;
}
?>

Example #4 Class constant visibility modifiers, as of PHP 7.1.0

<?php
class Foo {
    public const BAR = 'bar';
    private const BAZ = 'baz';
}
echo Foo::BAR, PHP_EOL;
echo Foo::BAZ, PHP_EOL;
?>

bar

Fatal error: Uncaught Error: Cannot access private const Foo::BAZ in …