Canon MTF Question

I can't find a definitive answer to one simple question re: Canon MTF charts:


Do the black lines mean "wide open" or do they always represent f/2.8?


I assume they must mean "wide open" because of course some lenses only open up to f/4...but it'd be nice to get a clear answer.


Looking at the 35L for example...


http://www.usa.canon.com/cusa/professional/products/professional_cameras/ef_lens_lineup/lens_wide_pro/ef_35mm_f_1_4l_usm#Overview


Thanks!

The black lines means wide open.

Grazie.