Fac IPO?

I was wondering what does the “Fac” IPO do for sequences? i was thinking it meant factor of the intensity of the infunence of a proticular Sequence.
and when i set curve for it to test it on the ‘glow’ sequence, i animated no effect. so im curious what does it do and effect?

it’s Frame At …something something something
in the plugin itself the fac0 parameter is a value between 0 and 1 that indicates where in the strip it is - useful for fades and similar, to know how much fading to do.

The IPO curve overrides that value. So eg you can apply an IPO to a crossfade so that it fades in and out a few times - 0 is fully the first strip and 1 is fully the second, 0.5 is halfway in between.