Enter the file type mask in the format offset, cb, mask, value.

A file type mask is part of a pattern registered under HKEY_CLASSES_ROOT\FileType\<CLSID>\<pattern>. Windows APIs such as OleCreateFromFile and GetClassFile can retrieve a class ID for a file by comparing information in this key to the bytes in the file. For example, 0,4,FFFFFFFF,AABBCCDD would mean that the first four bytes in the file must be AA BB CC DD for the system to use this component's class ID for a specified file.

You can specify more than one mask that the file has to match. Separate multiple patterns with a semicolon (;). When the setup creates these keys, the subkeys for each pattern are automatically numbered sequentially starting with 0 (zero).