<?php
/**
 * Define MyClass
 */
class MyClass
{
	//Declare a public constsnt
	public const MY_PUBLIC = 'public';

	// Declare a protected constant
	protected const MY_PROTECTED = 'protected';

	// Declare a private constant
	private const MY_PRIVATE = 'private';

	public function foo()
	{
		echo self::MY_PUBLIC;
		echo self::MY_PROTECTED;
		echo self::MY_PRIVATE;
	}
}

$myclass =new MyClass
MyClass::MY_PUBLIC;//works
MyClass::MY_PROTECTED;// Fatal Error
MyClass::MY_PRIVATE;// Fatal Error
$myclass->foo();// Public, Protected and Private work




/**
 * Define MyClass2
 */
class MyClass2 extends MyClass
{
	// This is public
	function foo2()
	{
		echo self::MY_PUBLIC;
		echo self::MY_PROTECTED;
		echo self::MY_PRIVATE;// Fatal Error
	}
}

$myclass2 = new MyClass2;
echo MyClass2::MY_PUBLIC;//works
$MyClass2->foo2();// Public and Protected work, not Private
?>