i am confused and don't get this to work.
here is a class : class Custom_HtmlEditorField_Toolbar extends Extension
it pushes a new radio-button to the link-dialog - popup on htmleditorfield.
also a sitetree- dropdown.

what i am trying to do is to add a checkbox, only visible when choosing the linkable-radio-button.
why is this checkbox hidden (display: none)???
any ideas?
thanks. timo.

class Custom_HtmlEditorField_Toolbar extends Extension{

	/**
	 * Aggiorna l'elenco delle possibili opzioni di link
	 * @param Form $form
	 * @return type
	 */
	public function updateLinkForm($form) {
		
		Requirements::javascript(LINKABLE_DATAOBJECTS_DIR . "/javascript/linkable-dataobjects.js");
		
		$fields = $form->Fields();
		/* @var $linkTipe CompositeField */
		$compositeField = $fields[1];
		/* @var $linkTipe OptionsetField */
		$linkTipe = $fields[1]->fieldByName("LinkType");
		
		$options = $linkTipe->getSource();
		
		$linkables = ClassInfo::implementorsOf('Linkable', 'replace_linkabledo');
		foreach ($linkables as $class) {
			
			$options[strtolower($class)] = $class::LinkLabel();
			$linkTipe->setSource($options);
			
			$replaceField = $fields[1];
			$checkbox = new CheckboxField('replace_linkabledo', 'Link mit DIV ersetzen?');
			$checkbox->addExtraClass('linkabledo', 'Linkable');
			$replaceField->push($checkbox);
			
			$dropdown = new DropdownField(strtolower($class), _t('HtmlEditorField.NEWS', $class::LinkLabel()), $class::get()->map('ID', 'Title'));
			$dropdown->addExtraClass('linkabledo');
			$compositeField->push($dropdown);
				
			
		}
		return $form;
	}
}