function week13_emailConfirm(emailField) {
  if (emailField.value != '') {
  
     var x = emailField.value;
     var filter = /^([a-zA-Z0-9_.-])+@(([a-zA-Z0-9-])+.)+([a-zA-Z0-9]{2,4})+$/;
     if (!filter.test(x)) {
        alert("The supplied email address appears to be invalid or incomplete. Please re-enter your email address.");
        emailField.value = '';
        emailField.focus();
     } 
  }
}

function week13_checkform()
{
	var valid = true;

	if (document.week13_form.week13_first.value == "") {
		alert('Please enter your first name.');
		valid = false;
	}
	if (document.week13_form.week13_email.value == "") {
		alert('Please enter your email address.');
		valid = false;
	}

	return valid;
}