When you select a file name in Windows 98, the file opens in an application
associated with that file type. The file is opened with the appropriate application
because the file extension is stored in the Registry with an association to that
application.
Each file type must have two entries in HKEY_CLASSES_ROOT. The first
entry defines the file extension and a name (name_ID) for this file type. This
name is then used in a second entry to define the commands for this file type. In
other words, one entry describes its extension and the other contains its properties.