MIME types are used to identify types of file. For example, a plain text file would have the MIME type 'text/plain'. An HTML page would be 'text/html' and a PNG image's type is 'image/png'. ROX-Filer uses MIME types to decide which application to run when you click on a file, and what icon to give it. ROX now uses the freedesktop.org Shared MIME Database to deal with MIME types. Ideally, the shared database will contain most of the types you need, and applications will add their own types to it automatically. However, sometimes you may need to edit the database manually, and MIME-Editor is a graphical editor for this. If a type is missing, consider asking for it to be added to the main database.