function cambiarImagen (obj, url) {
  obj.src = url;
}

function preloadImagen (url) {
  picture = new Image (1, 1);
  picture.src = url;
}

function cambiarClase (obj, clase) {
  obj.className = clase;
}

function ocultarObjeto (obj) {
  document.getElementById (obj).style.visibility = 'hidden';
  try {
    WCH.Discard (obj);
  } catch (e) { }
}

function mostrarObjeto (obj) {
  try {
    WCH.Apply (obj, true);
  } catch (e) { }
  document.getElementById (obj).style.visibility = 'visible';
}

function validarEMail (str) {

  var at = "@"
  var dot = "."
  var lat = str.indexOf (at)
  var lstr = str.length
  var ldot = str.indexOf (dot)

  if (lstr == 0) return true;
  if (str.indexOf (at) == -1) return false;
  if (str.indexOf (at) == -1 || str.indexOf (at) == 0 || str.indexOf (at) == lstr) return false;
  if (str.indexOf (dot) == -1 || str.indexOf (dot) == 0 || str.indexOf (dot) == lstr) return false;
  if (str.indexOf (at, (lat+1)) != -1) return false;
  if (str.substring (lat-1, lat) == dot || str.substring (lat+1, lat+2) == dot) return false;
  if (str.indexOf (dot, (lat+2)) == -1) return false;
  if (str.indexOf (" ") != -1) return false;

  return true

}

function mascaraFecha (obj, evt) {

  var charCode = (evt.which) ? evt.which : event.keyCode
  var valor = true;
  if (charCode > 31 && (charCode < 48 || charCode > 57)) valor = false;
  if ((obj.value.length == 2) || (obj.value.length == 5)) obj.value = obj.value + "/";
  return (valor);

}