function get_xmlHTTP_object() {
	var xml_http;
	try {	//IE
		xml_http = new ActiveXObject("Msxml2.XMLHTTP");
	}
	catch (e) {	//other browsers
		xml_http = new XMLHttpRequest();
	}
	return xml_http;
}

//expand or hide the top level chapters
function expand_chapter(chapterID) {

	
	//if the chapter is displayed, hide it
	if (document.getElementById('ch_' + chapterID).style.display == 'block') {
		document.getElementById('ch_' + chapterID).style.display = 'none';
		document.getElementById('I' + chapterID + 'sign').src = '/images/plus.gif';
		document.getElementById('I' + chapterID).src = '/images/folder.gif';
	}
	//else, show it
	else {
		//put the loading graphic in div_status
		document.getElementById('ch_' + chapterID).innerHTML = '<img src="/images/loading_blue.gif" />';
		document.getElementById('ch_' + chapterID).style.display = 'block';
		
		//get the html from server
		var xml_http = get_xmlHTTP_object();		
		
		//set the ready-state function to populate the chapter-node with the html from the server
		xml_http.onreadystatechange = function() {
			if (xml_http.readyState == 4) {
				//show chapter contents
				document.getElementById('ch_' + chapterID).innerHTML = '';
				document.getElementById('ch_' + chapterID).innerHTML = '<span>' + xml_http.responseText + '</span>';
				//change image
				document.getElementById('I' + chapterID + 'sign').src = '/images/minus.gif';
				document.getElementById('I' + chapterID).src = '/images/base.gif';
			}
		}
		
		//run the server-side code	
		var url = '/planning_guide/xmlOpenChapter.aspx?ch=' + chapterID;
		xml_http.open("GET", url, true);
		xml_http.send(null);		
		
	}
}