var tam=13;
	function mudaFonte(tipo)
	{
		if (tipo=="mais")
		{		
			tam+=1;
		}
		else
		{
			tam-=1;
		} 
		document.getElementById('tx').style.fontSize=tam+'px' ;
	}
	
function abreJanela(pagina, nome, w, h, rolagem) {
var winl = (window.screen.availWidth/2)-(w/2);
var wint = (window.screen.availHeight/2)-(h/2)-12;
var winProps = 'height='+h+',width='+w+',top='+wint+',left='+winl+',scrollbars='+rolagem+',resizable=no';
win = window.open(pagina, nome, winProps)
win.window.focus();
}