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

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