function show_tip (id) {
		el = document.getElementById('tip'+id);
		if (el.style.visibility == 'visible') {
			el.style.visibility = 'hidden';
			el.style.position = 'absolute';
		}
		else {
			el.style.visibility = 'visible';
			el.style.position = 'relative';
		}
	}
	
	function isEmailAddr(email)
{
  var result = false;
  var stringEmail = new String(email);
  var index = stringEmail.indexOf("@"); 
  if (index > 0) 
  {
    var pindex = stringEmail.indexOf(".",index);  
																										
    if ((pindex > index+1) && (stringEmail.length > pindex+1)) 
	result = true; 
  }
  if (!result) alert("Escreva um email válido.");
  return result;  
}