function setNavDisplay(headerName){
	// toggle navigation elements display between visible and hidden
	if(document.all){
		if (document.all(headerName).style.display == 'none')
			document.all(headerName).style.display = '';
		else
			document.all(headerName).style.display = 'none';
	}
	else if(document.getElementById){
		if (document.getElementById(headerName).style.display == 'none')
			document.getElementById(headerName).style.display = '';
		else
			document.getElementById(headerName).style.display = 'none';
	}
}