title: simple Ajax (local): responseText is empty
body: <p>I've tried to use an example from a tutorial, but the response text is just empty. If I try with 'alert' I get <code>OK</code>, but with the responseText, the popup is just empty, nothing in it. Why is this?</p>
  
  <pre><code>function start(){  
  var xhr = getXMLHttpRequest();  
  var sVar1 = encodeURIComponent("firstContent");  
  var sVar2 = encodeURIComponent("SecondContent");  
  xhr.onreadystatechange = function() {  
      if (xhr.readyState == 4 &amp;&amp; (xhr.status == 200 || xhr.status == 0)) {  
          //alert("OK");  
                  alert(xhr.responseText);  
      }  
  }; 
  
  
  
  xhr.open("GET", "handlingData.php?variable1=" + sVar1 + "&amp;variable2= " + sVar2, true);  
  xhr.send(null);  
  }  
  </code></pre>
  
  <p>The function 'start' is called by the onsubmit: </p>
  
  <pre><code>form id="form_userlogin" onsubmit="start()"  
  </code></pre>
  
  <p>And the PHP page:  </p>
  
  <pre><code>&lt;?php
  header("Content-Type: text/plain");  
  $variable1 = (isset($_GET["variable1"])) ? $_GET["variable1"] : NULL;  
  $variable2 = (isset($_GET["variable2"])) ? $_GET["variable2"] : NULL;  
  if ($variable1 &amp;&amp; $variable2) {  
      echo "OK";  
  } else {  
      echo "FAIL";  
  }  
  ?&gt;   
  </code></pre>
  
  <p>I thought it would be ok to follow the tutorial, but it's not ;p
  Can you please tell me if you see something wrong?</p>