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     FormField::setup()
 * @since   3.2
 */
public function setup(\SimpleXMLElement $element, $value, $group = null)
{
    $return = parent::setup($element, $value, $group);
    if ($return) {
        $this->keyField = (string) $this->element['key_field'];
    }
    return $return;
}