Although `offsetSet` is supposed to be an alias to `attach`, real-world results do not indicate that. When extending the SplObjectStorage class, it's expected that a modification to `attach` would also affect `offsetSet`. However, it seems they need to both be extended. Consider the results below...

<?php

declare(strict_types=1);

class CustomSplObjectStorage extends SplObjectStorage
{
    public function offsetSet(mixed $object, mixed $info = null): void
    {
        print("offsetSet called\n");
        parent::offsetSet($object, $info);
    }

    public function attach(mixed $object, mixed $info = null): void
    {
        print("attach called\n");
        parent::attach($object, $info);
    }
}

$a = new CustomSplObjectStorage();
$a[new stdClass()] = 'ok';
$a->attach(new stdClass(), 'ok');
?>

This prints:
```
offsetSet called
attach called
```

While we would expect...

```
offsetSet called
attach called
attach called
```

... if `offsetSet` was a true alias of `attach`. I'm not sure if this is intentional or not.