* The value is, e.g. lang <br>
     * comment: Field name for language in the index.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexFieldLang();

    /**
     * Get the value for the key 'index.field.has_cache'. <br>
     * The value is, e.g. has_cache <br>
     * comment: Field name for cache status in the index.