Method setup

/**
 * Method to attach a Form object to the field.
 *
 * @param   \SimpleXMLElement  $element  The SimpleXMLElement object representing the `<field>` tag for the form field object.
 * @param   mixed              $value    The form field value to validate.
 * @param   string             $group    The field name group control value. This acts as an array container for the field.
 *                                      For example if the field has name="foo" and the group value is set to "bar" then the
 *                                      full field name would end up being "bar[foo]".
 *
 * @return  boolean  True on success.
 *
 * @see     \Joomla\CMS\Form\FormField::setup()
 * @since   4.0.0
 */
public function setup(\SimpleXMLElement $element, $value, $group = null)
{
    $return = parent::setup($element, $value, $group);
    if ($return) {
        // Note: $this->element['optionsFilter'] is not cast to string here to allow empty string value.
        $this->optionsFilter = $this->element['optionsFilter'] ? explode(',', (string) $this->element['optionsFilter']) : [];
    }
    return $return;
}