Hi,
Before I start to use jquery for form validation, I wonder if I could user RequiredFields to check if a CheckboxField is selected .
The next code is not validating the CheckboxField :

function SubscriptionForm() {
		$condition =FormPage::ConditionDetails();
		$url = $condition->URLSegment;
		
		$fields = new FieldSet(
			new HiddenField("Subject", "Subject", $this->CF_Title),
			new TextField("Name", "Naam"),
			new CheckboxField("CheckThis","Ckeck this box")
		);

		$actions = new FieldSet(
					new FormAction('SendSubscriptionForm', 'Send')
			);

		$validator = new RequiredFields('Name','CheckThis');
				
		$form =  new Form($this, "SubscriptionForm", $fields, $actions, $validator); 
		return $form;
	}

Seems ok, but maybe i missed something.

Thanks in advance..

RequiredFields needs to be passed an array of fieldnames, not a string

new RequiredFields(array('Name', 'CheckThis'));

You replied before I edited the post, but you were right about the typo.

I noticed that the checkboxes do validate serverside after form submission, but not onClick with the Textfields.

However, I can live with it for the moment...