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