[gentoo-dev] ebuild dependencies

[Zach Forrest]

After looking through some ebuild files, I have noticed that some of the 
depends entries have a question mark after them. I'm not exatly sure 
what this means, but it seems like an optional dependency, maybe for a 
use flag?

Example:
decss? ( media-libs/libdvdcss )

If someone wouldn't mind giving me a quick how-to, I would really 
appreciate it.

Thanks.

Zach