protected function handleLoadCallback($field, $value)
    {
        // Load callback.
        if (isset($field['load_callback']) && is_array($field['load_callback'])) {
            foreach ($field['load_callback'] as $callback) {
                $this->import($callback[0]);
                $value = $this->{$callback[0]}->{$callback[1]}($value, $this);
            }
        }

        return $value;
    }