This is the default FileHandler that will be invoked when no other can be found to handle a file. It is embedded in the library and thus always available (as opposed to plugin FileHandlers which might not always be available, depending on the configuration).
It is also used by default in the browser window (in the right lower pane) to display the information of the currently selected item in the directory tree or file list.
It can be explicitly invoked for any file system entry by selecting it from that items context menu (accessible through right clicking it).
In case of showing information about a directory, a button allows to scan its contents and report the sum of its files, subfolders and the amount of overall occupied space.