title: Undefined index on form submit
body: <p>I write a selection of ids (e.g. "3,4,31") in a disabled <code>textarea</code> (works fine so far) and want to submit that via GET.
  I don't understand why I keep getting an undefined index error with the following code:</p>
  
  <pre><code>&lt;form action="slider/Jssor/image-gallery.source.php" method="get"&gt;&lt;br&gt;
    &lt;textarea name="selection" id="result" disabled&gt;&lt;/textarea&gt;
    &lt;input type="submit" value="Jssor Imgage Gallery"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p><code>image-gallery.source.php</code> throws the undefined index error when calling:</p>
  
  <pre><code>&lt;?php
    echo $_GET["selection"];
  ?&gt;
  </code></pre>
  
  <p>The link to the new page works fine so I assume it can't be because of the path in the action attribute!? 
  I don't see the Ids transported in the URL (?selection=3,4,31), so what am I doing wrong?</p>