The headliner bows insert behind this edge. There is a Notched area inside this groove that the bow MUST sit inside of. Make sure the bow is not free floating.
Four areas where the trim starts/stops. When cutting vinyl for these areas, angle your scissors to get a beveled edge on the vinyl. The vinyl edge looks neated this way once installed. If using tweed, fold the raw edge but cut to single thickness when rolling inside the window lip.
The main headliner goes in first, before any of the window trim pieces. This shows the transition of the headliner onto the B Pillar. Above the driver door the headliner is tucked under the gripper teeth. (pass door and slider also).