function navigation(){
	
	//highlight relevant links
	if(window.nav && document.getElementById("nav-" + nav)){
		document.getElementById("nav-" + nav).className = "on";
	}
	if(window.sub_nav && document.getElementById("sub-nav-" + sub_nav)){
		document.getElementById("sub-nav-" + sub_nav).className = "on";
	}

}