silverstripe-userforms/code/model/editableformfields/EditableFieldGroup.php

<?php

/**
 * Specifies that this ends a group of fields
 */
class EditableFieldGroup extends EditableFormField {

	private static $has_one = array(
		'End' => 'EditableFieldGroupEnd'
	);

	/**
	 * Disable selection of group class
	 *
	 * @config
	 * @var bool
	 */
	private static $hidden = true;

	/**
	 * Non-data field type
	 *
	 * @var type
	 */
	private static $literal = true;

	public function getCMSFields() {
		$fields = parent::getCMSFields();
		$fields->removeByName(array('MergeField', 'Default', 'Validation', 'DisplayRules'));
		return $fields;
	}

	public function getCMSTitle() {
		$title = $this->getFieldNumber()
			?: $this->Title
			?: 'group';

		return _t(
			'EditableFieldGroupEnd.FIELD_GROUP_START',
			'Group {group}',
			array(
				'group' => $title
			)
		);
	}

	public function getInlineClassnameField($column, $fieldClasses) {
		return new LabelField($column, $this->CMSTitle);
	}

	public function showInReports() {
		return false;
	}

	public function getFormField() {
		$field = UserFormsGroupField::create()
			->setTitle($this->EscapedTitle ?: false)
			->setName($this->Name);
		$this->doUpdateFormField($field);
		return $field;
	}

	protected function updateFormField($field) {
		// set the right title on this field
		if($this->RightTitle) {
			// Since this field expects raw html, safely escape the user data prior
			$field->setRightTitle(Convert::raw2xml($this->RightTitle));
		}

		// if this field has an extra class
		if($this->ExtraClass) {
			$field->addExtraClass($this->ExtraClass);
		}
	}

	protected function onBeforeDelete() {
		parent::onBeforeDelete();

		// Ensures EndID is lazy-loaded for onAfterDelete
		$this->EndID;
	}

	protected function onAfterDelete() {
		parent::onAfterDelete();

		// Delete end
		if(($end = $this->End()) && $end->exists()) {
			$end->delete();
		}
	}

}