errors views and helpers

you need to load url helper from config/autoload.php to use this helper function.
set as below:
$autoload['helper'] = array('url');

I know how these helpers work. But my problem is that, in codeigniter errors views, it's not possible to use helpers functions. Why?
Try it yourself, you 'll see that you can't use neither codeigniter native helpers functions, nor your own functions in errors views.

Simplicity is the ultimate sophistication