torque/Aegisub-Motion — comment on commit b17082dbc1fd6cee5773c7c656f73ebe00b80b26
File: Aegisub-Motion.lua line 908
By torque:

vsfilter supports \clip(n,) notation, where n is a scaling factor that divides all points in the clip object by 2^(n-1). This *potentially* allows for subpixel clips, as the clip object itself can only contain integers. It may or may not actually help in practice when the clip is being scaled down or is panning slowly (situations where rounding errors would become more obvious). Unfortunately libass doesn't support this, so it's only applied if the initial clip contains a scaling factor (which is why it's wrapped in an if).