[css3-fonts] font-size-adjust and em/ex values

We need a sentence in CSS3 Fonts that says whether font-relative lengths
are calculated against the [computed? used? something else?] font-size.

I'm pretty sure 'em' should always calculate against the specified
font-size. however I'm less sure of the other values; it seems like
taking font-size-adjust into account would be better for measurements
against the ex-height or font pitch.

~fantasai