This option can be used to exclude all file names but those matching the specified regexp pattern. This enables you to for example deny all but the specific file extensions specified.

Example of usage in the config.php file

$mcFileManagerConfig['download.include_file_pattern'] = "/^onlythis$|^onlythat$/i";

Example of usage in the Web.Config file

<add key="download.include_file_pattern" value="/^onlythis$|^onlythat$/i" /> 

Example of usage in a mc_access file