The "Extensions" screen registers and changes file extensions. A file extension is an addition at the end of a file name that indicates the type of file. The extension consists of one or more letters, usually three, after the last dot in the name. In the file name `contract.doc`, for example, `.doc` is the file extension. Most operating systems use file extensions to determine the type of a file, so that they can start the appropriate program to open it. The entry fields are: - "Code": The code of the extension. - "Description": The description of the extension, for example the program that opens the extension or the function of files with this extension. - "MIME Type": The reference to the MIME type as registered in [[Invantive Estate/Subjects/Advanced/MIME Types|MIME Types]].