Self vs Static in PHP

self.static.php

<?php
class A 
{
    public static $var = "I'm set in A!<br>";
    
    public static function getStatic() {
        echo static::$var;
    }
    
    public static function getSelf() {
        echo self::$var;
    }
}

class B extends A 
{
    public static $var = "I'm set in B!<br>";
}

B::getSelf();    // I'm set in A!
B::getStatic();  // I'm set in B!