ob_gzhandler modes

Hi,

I am using ob_gzhandler to compress my web pages.
"Normal" using of ob_gzhandler is easy and no problems there.

I however have one problem and that is the modes that can be selected using ob_gzhandler.

Since it is defined like:
string ob_gzhandler ( string buffer [, int mode])

So does anyone know what are those modes and where they are documented?

I've tried to search forums, web pages etc. but found nothing at all about the modes :/

Thanks!