MIME Types

GTKtalog uses MIME types to store the file types. So does Gnome, Kde ... The MIME type of a file is determined by the extension or by the content (best).

A MIME type is a string such as "application/zip" for (.zip files) or "image/jpeg" for (.jpg files)

In four places within GTKtalog, you are asked to type a MIME type (all in the preferences):

If you don't know the Mime string but you know the extension, use the button "Guess from an extension". Give an extension, it will return the corresponding Mime type .... cool !

If there is no known MIME type for your extension, you'll have to add it in the Gnome control center : Document Handlers/File types and programs. See the Gnome Control Center documentation for more information.