<?php
spl_autoload_register(function ($name) {
    echo("AUTOLOAD '$name'\n");
    eval("class $name {}");
});

class BASE {
}

interface I {
}

class A extends BASE implements I {
}

$a = new A;
var_dump(is_a($a, "B1"));
var_dump(is_a($a, "A"));
var_dump(is_a($a, "BASE"));
var_dump(is_a($a, "I"));
var_dump(is_subclass_of($a, "B2"));
var_dump(is_subclass_of($a, "A"));
var_dump(is_subclass_of($a, "BASE"));
var_dump(is_subclass_of($a, "I"));

var_dump(is_subclass_of("X1", "X2"));
?>