PHP upload - Why isset($_POST['submit']) is always FALSE
<p>I have the following code sample upload3.php:</p>

<pre><code>&lt;html&gt;
&lt;head&gt;
&lt;title&gt;PHP Form Upload&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;form method='post' action='upload3.php' enctype='multipart/form-data'&gt;
    Select a File:
    &lt;input type='file' name='filename' size='10' /&gt;
    &lt;input type='submit' value='Upload' /&gt;
&lt;/form&gt;

&lt;?php

if (isset($_POST['submit']))
{
    echo "isset submit";
}
else 
{
    echo "NOT isset submit";
}

?&gt;

&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>The code always returns "NOT isset submit".
Why does this happen? Because the same script upload3.php calls itself?</p>
