//the first parameter gives the id to the content to be shown; the second parameter gives the id to the content to be hidden
function showMenu (idNew, idOld) {
	if (idNew != null) {
		try { document.getElementById(idNew).style.display = 'block'; } catch (e1) { }
	}
	
	if (idOld != null) {
		try { document.getElementById(idOld).style.display = 'none'; } catch (e2) { }
	}
}