public function getCopyFieldDefinitions()
    {
        $xml = array();

        // Default copy fields
        foreach ($this->getCopyDestinations() as $copyTo) {
            foreach ($this->fulltextFields as $name => $field) {
                $xml[] = "<copyField source='{$name}' dest='{$copyTo}' />";
            }
        }

        // Explicit copy fields
        foreach ($this->copyFields as $source => $fields) {
            foreach ($fields as $fieldAttrs) {
                $xml[] = $this->toXmlTag('copyField', $fieldAttrs);
            }
        }

        return implode("\n\t", $xml);
    }