function fn_HideElement( elementName ){
	ele = document.getElementById( elementName );
	if( ! ele ){
		alert( 'cannot find ' + elementName );
		return;
		}
	ele.style.display = "none";
	}
function fn_ShowElement( elementName ){
	ele = document.getElementById( elementName );
	if( ! ele ){
		alert( 'cannot find ' + elementName );
		return;
		}
	ele.style.display = "block";
	}