function ltrim(s) {     
  return s.replace(/^\s+/, ""); 
}
function rtrim(s) {     
  return s.replace(/\s+$/, ""); 
}
function trim(s) {     
  return rtrim(ltrim(s)); 
}
function validarMail(mail) {
  var filtro = /^[A-Za-z][A-Za-z0-9_]*@[A-Za-z0-9_]+\.[A-Za-z0-9_.]+[A-za-z]$/;
  if (filtro.test(mail)) {
    return true;
  }
  else {
    return false;
  }
}
function permitirSoloNumeros(evt) {
  // NOTE: Backspace = 8, Enter = 13, '0' = 48, '9' = 57  
  var key = nav4 ? evt.which : evt.keyCode;  
  return (key <= 13 || (key >= 48 && key <= 57));       
}