JSI Tip 9152. Common file type Value Names and sub-keys.

File types, like .txt or .jpg are defined in the registry at HKEY_CLASSES_ROOT\.EXT, where .EXT represents the file extension, like HKEY_CLASSES_ROOT\.txt or HKEY_CLASSES_ROOT\.jpg.

NOTE: It is important to include the leading period.

The common Value Names and sub-keys of a file type, HKEY_CLASSES_ROOT\.EXT, are:

    Default Value   This string data type sets the PROGID, like txtfile or jpegfile. see HKEY_CLASSES_ROOT\txtfile.

    PerceivedType   This string data type, not used prior to Windows XP, defines the preceived type, if any, and may be:
                           Image
                           Text
                           Audio
                           Video
                           Compressed
                           System
 
    Content Type    This sting data type is the MIME content type, like audio/aiff or text/plain. 
                    See HKEY_CLASSES_ROOT\MIME\Database\Content Type.

    OpenWithProgids This subkey contains a list of alternate PROGIDs for this file type. They populate the Open With dialog.
                    The Value Names, like AIFFFile and jpegfile are REG_NONE data types.

    OpenWithList    This subkey contains application subkeys that populate the Open With dialog, like wmplayer.exe.
                    The application must exist at HKEY_CLASSES_ROOT\AppID, like: 
                                 HKEY_CLASSES_ROOT\AppID\wmplayer.exe
                                       AppID       REG_SZ  \{B8C54A54-355E-11D3-83EB-00A0C92A2F2D\}