/* function that opens a new window without the navigation elements.
 * this approach has the advantage that subsequently opened virtuallab
 * examples are all directed to the same window and thus prevent 
 * cluttering of screen.
 */
function runLab(url) {
	lab = window.open(url,"VirtualLab","scrollbars,width=600,height=680");
}

/* the stripe() script is based on an example found at http://www.alistapart.com/
 * an excellent source of tips for advanced css techniques.
 * the script below add coloring of header cells
 */
// this function is needed to work around 
// a bug in IE related to element attributes
function hasClass(obj) {
	var result = false;
	if (obj.getAttributeNode("class") != null) {
		result = obj.getAttributeNode("class").value;
	}
	return result;
}   

/* function to underlay tables with stripes of different color as a visual
 * aid to keep track of the data.
 * arguments:
 * id: id of table element - accepts also a list of comma separated ids
 * color: color of even numbered rows (optional)
 * color: color of odd numbered rows (optional)
 */
function stripe(ids) {

	// the flag we'll use to keep track of 
	// whether the current row is odd or even
	var even = false;

	// if arguments are provided to specify the colours
	// of the even & odd rows, then use the them;
	// otherwise use the following defaults:
	var evenColor = arguments[1] ? arguments[1] : "#fff";
//	var oddColor = arguments[2] ? arguments[2] : "#e9e9e9";
	var oddColor = arguments[2] ? arguments[2] : "#ffe8e5";

	var idlist = ids.split(',');
	if( !idlist ) { return; }

	for( var idx=0; idx<idlist.length; idx++ ) {
	id = idlist[idx].replace(/^\s*/, '');
	
	// obtain a reference to the desired table
	// if no such table exists, abort
	var table = document.getElementById(id);
	if (! table) { return; }
	
	// reset coloring
	even = false;

	// by definition, tables can have more than one tbody
	// element, so we'll have to get the list of child
	// &lt;tbody&gt;s 
	var tbodies = table.getElementsByTagName("tbody");

	// and iterate through them...
	for (var h = 0; h < tbodies.length; h++) {
    
		// find all the &lt;tr&gt; elements... 
		var trs = tbodies[h].getElementsByTagName("tr");

		// ... and iterate through them
		for (var i = 0; i < trs.length; i++) {

		// avoid rows that have a class attribute
		// or backgroundColor style
		if (! hasClass(trs[i]) &&
			! trs[i].style.backgroundColor) {

			// get all the cells in this row...
			var tds = trs[i].getElementsByTagName("td");

			// and iterate through them...
			for (var j = 0; j < tds.length; j++) {

				var mytd = tds[j];

				// avoid cells that have a class attribute
				// or backgroundColor style
				if (! hasClass(mytd) &&
					! mytd.style.backgroundColor) {

					mytd.style.backgroundColor =
						even ? evenColor : oddColor;
				}
			}

			// get all the headers in this row...
			var ths = trs[i].getElementsByTagName("th");

			// and iterate through them...
			for (var j = 0; j < ths.length; j++) {

				var myth = ths[j];

				// avoid cells that have a class attribute
				// or backgroundColor style
				if (! hasClass(myth) &&
					! myth.style.backgroundColor) {

					myth.style.backgroundColor =
						even ? evenColor : oddColor;
				}
			}
		}
		// flip from odd to even, or vice-versa
		even =  ! even;
		}
	}
	}
}