public function getContentById($identifier, $default = null)
    {
        if (empty($this->registry[$this->section][$identifier])) {

            $this->registry[$this->section][$identifier] = $this->getContentByIds(array($identifier));

            if (empty($this->registry[$this->section][$identifier])) {
                return $default;
            }
        }

        return $this->registry[$this->section][$identifier];
    }