function isValidEmail(checkStr)
{
  // test valid email address
  var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9])+$/;
  var EmailValid = filter.test(checkStr);
  return (EmailValid);
}

function checkSubscribeForm(theForm)
{
  var emailField = theForm.txtEmail;

  // check to see if the Email Address is blank
  if (emailField.value == "")
  {
    alert("Vyplňte laskavě vaši e-mailovou adresu.");
    emailField.focus();
    return (false);
  }
  // check email address length
  if (emailField.value.length > 100)
  {
    alert("Zadejte laskavě adresu kratší než 100 znaků.");
    emailField.focus();
    return (false);
  }
  // check email address structure
  if (!isValidEmail(emailField.value))
  {
    alert("Zadaná adresa " + emailField.value + " není platná. Zkuste ji laskavě vyplnit znovu.");
    emailField.focus();
    return (false);
  }
  return (true);
}

function openWindow(url) {
	mywin = window.open(url,'','toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1,width=640,height=480,alwaysRaised=yes');
	mywin.focus();
}