title: filling innerhtml of dropdown menu with specific data
body: <p>I have a xmlhttp/php problem. I have one drop-down menu where people are able to select municipality. Then I want to return a list of possible options within that municipality to a secondary drop-down menu.</p>
  
  <p>people first select a municipality (html code below):</p>
  
  <pre><code>&lt;select name="pszplaats" id="gemeente" onchange="fdisplay();loadXMLDoc(this.value)"&gt;
      &lt;?php while($row=mysql_fetch_array($selectgem)){?&gt;
      &lt;option value="&lt;?php echo $row['Gemeente']; ?&gt;"&gt;&lt;?php echo $row['Gemeente'];?&gt;
      &lt;/option&gt;
       &lt;?php } ?&gt;
      &lt;/select&gt;
  </code></pre>
  
  <p>loadXMLDoc is the function that should send this answer to the (php-)server and retreive a list of names matching those in that municipality. 
  so far my relevant java/xml/ajax code is this:</p>
  
  <pre><code>function loadXMLDoc() {
        var xmlhttp;
        gem=document.getElementById("gemeente").value;
        if (window.XMLHttpRequest)
           {// code for IE7+, Firefox, Chrome, Opera, Safari
           xmlhttp=new XMLHttpRequest();
           }
        else
            {// code for IE6, IE5
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
            }
            xmlhttp.onreadystatechange=function(){
                   if (xmlhttp.readyState==4 &amp;&amp; xmlhttp.status==200)
                   {
                   document.getElementById("test").innerHTML=xmlhttp.responseText;
                   }
             }
        xmlhttp.open("POST","http://www.doenwatikkan.nl/jeroen/dynamic.php",true);
        xmlhttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
        xmlhttp.send();
        alert(gem)
  
             }
  </code></pre>
  
  <p>Alert(gem) shows the selected option, so I know that at least this works.
  the php to retreive the right values is this:</p>
  
  <pre><code>$gem=$_POST["pszplaats"];
  $gennam=mysql_query("SELECT * FROM psz WHERE Gemeente=$gem");
  echo $gennam["$gem"];
  </code></pre>
  
  <p>now the problem lies in the filling of the secondary drow-down menu</p>
  
  <pre><code>&lt;select name="psznaam" id="test" style="display:none"&gt;
  &lt;?php while($row=mysql_fetch_array($selectall)){?&gt;
  &lt;option value="&lt;?php echo $row['NaamPSZ']; ?&gt;"&gt;&lt;?php echo $row['NaamPSZ'];?&gt;
  &lt;/option&gt;
  &lt;?php } ?&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>after the java function is finished the drop-down menu is completely empty. Can anybody tel me how I can actually get the relevant data in that menu?
  any help would be much appreciated!</p>