function openPrelistening(contentid) {
        var httpRequest;

        if (window.XMLHttpRequest) { // Mozilla, Safari, ...
            httpRequest = new XMLHttpRequest();
            if (httpRequest.overrideMimeType) {
                httpRequest.overrideMimeType('text/xml');
                // See note below about this line
            }
        } 
        else if (window.ActiveXObject) { // IE
            try {
                httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
                } 
                catch (e) {
                           try {
                                httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
                               } 
                             catch (e) {}
                          }
                                       }

        if (!httpRequest) {
            alert('Giving up :( Cannot create an XMLHTTP instance');
            return false;
        }

		//removeElement();
		
        httpRequest.onreadystatechange = function() { alertPrelistening(httpRequest, contentid); };
		var url = './ajax_prelistening.php?contentid='+contentid;
        httpRequest.open('GET', url, true);
        httpRequest.send('');

    }	
	
    function alertPrelistening(httpRequest, number) {

	//0: not initialized.
	//1: connection established.
	//2: request received.
	//3: answer in process.
	//4: finished.

        if (httpRequest.readyState == 4) {
            if (httpRequest.status == 200) {
			
			  removeElement();
			  // then add
			  var ni = document.getElementById('pre'+number);
			  var newdiv = document.createElement('div');
			  newdiv.setAttribute('id','mypre');
			  newdiv.innerHTML = httpRequest.responseText;
			  ni.appendChild(newdiv);		
			  
		  
			  
			  var oldnumber = document.getElementById('myvalue');
	  		  if (oldnumber != null) 
	  		  {
				  document.getElementById('myvalue').value = number;
			  } else {
				  var ni = document.getElementById('content');
				  var newinput = document.createElement('input');
				  newinput.setAttribute('id','myvalue');
				  newinput.setAttribute('value',number);
				  newinput.setAttribute('type','hidden');
				  ni.appendChild(newinput);
			  }
				
            } else {
                alert('There was a problem with the request.');

            }
			
        }
    }		
	
	function removeElement() {
	  var oldnumber = document.getElementById('myvalue');
	  if (oldnumber != null) 
	  {
		  var number = document.getElementById('myvalue').value;
		  var d = document.getElementById('pre'+number);
		  var olddiv   = document.getElementById('mypre');
		  var olddiv_o = document.getElementById('mypre_o');
		  if (olddiv != null)
		  {
			d.removeChild(olddiv);
			
		  }
	  }
	}