function toggle_SubContent(id) {
		 /* all # page contents off */
		var c1 = document.getElementById('Sub_Intro');  c1.style.display = 'none';
		var c2 = document.getElementById('Sub_1');      c2.style.display = 'none';
		var c3 = document.getElementById('Sub_2');      c3.style.display = 'none';
		var c4 = document.getElementById('Sub_3');      c4.style.display = 'none';
		var c4 = document.getElementById('Sub_4');      c4.style.display = 'none';
		var c4 = document.getElementById('Sub_5');      c4.style.display = 'none';
		/* toggle only content we want ON */
		var e  = document.getElementById(id); e.style.display = 'block';
		}