What exactly laravel's isValid method does?
<p>I was reading the Laravel's docs and I've stumbled upon this isValid() method, that returns TRUE or FALSE whether the file is valid or not.</p>

<p>But... What this method actually does? I know it returns TRUE or FALSE, but what is behind this check? Over what is checking if is valid or not? I've googled for a while but can't really find something useful...</p>

<p>Can you guys explain me this?</p>

<p>Thanks!</p>