Why $_SERVER['HTTP_HOST'] sometimes return uppercase?
<p>I use <code>$_SERVER['HTTP_HOST']</code> to check my script running on correct domain and send an email when it runs on illegal domain. The problem is that sometimes I receive incorrect alerts that script run on incorrect domain. It is a false alert with <code>$_SERVER['HTTP_HOST']</code> in uppercase.</p>

<p>First, why this happen?
Second, is this safe to check <code>$_SERVER['HTTP_HOST']</code> or is there a better why?</p>

<p>Note: I didn't convert value to lowercase in my code.</p>
