function switch_tabs(tab) {
	var tabs = document.getElementById('demtabnav').getElementsByTagName('li').length;
	//switch off all tabs and content
	for (i=0; i < tabs; i++) {
		document.getElementById('demtab'+(i+1)).className = '';
		document.getElementById('demtab'+(i+1)+'_con').style.display = 'none';
	}
	//switch on the selected tab and content
	document.getElementById(tab).className = 'demtabsel';
	document.getElementById(tab+'_con').style.display = 'block';
}