questions

"Private Download provides a private download directory for use when the file system is configured for public download access."

How will hook_file_download run if file system is public?

http://api.drupal.org/api/drupal/developer!hooks!core.php/function/hook_...

It says: This hook allows modules enforce permissions on file downloads when the private file download method is selected.

Mybe dont i understand sg?

If my file path is sites/dev.example.com/files and private dowload dir is private how can i modify my RewriteBase path.
In this case my private download dir will be sites/dev.example.com/files/private and i cant rewrite my rewritebase path cos it requires "/system/files/". $form_state['values']['private_download_directory'] to be existing. Thx.