In WIP V9 BlendSrf if Zebra is active and the input surfaces are selected then zebra stripes are also shown for the blend surface and the zebra stripe settings can be changed while BlendSrf is active. However it is not possible start Zebra nor add surfaces for zebra stripes while BlendSrf is active.
In WIP V9 MatchSrf has a button so show the zebra stripes, but the settings cannot be adjusted, even if the Zebra panel is diplayed.