Drag & Drop: Only continue, if all have been dropped on targets

Update:

I got it to work by

• using drop-triggers to set drop-check-variables to true if items are dropped (one for each)
• using "in" intersect-triggers (area covers the original positions) to set drop-check-variables to false if items are returned to their original position
• using "out of" intersect-triggers (area covers the drop target positions) to set drop-check-variables to false if items are returned to their original position
  (yes both intersect checks are needed for a reliable result, otherwise fast-dragging will cause problems)

Disadvantages:

• only works with manual position reset (so if the "one per target" is used, SL resets automatically and that sadly isn't processed/recognized by SL for intersection triggers)
• performance for drag-drop is lower (at least on some browsers), since so much needs to be checked by triggers in realtime it seems
• this is a complex, error-prone workaround if something changes in the future and takes a lot of time to set up and check

I'd wish for an easier more reliable solution in the future. Like using (new) states of the drag-drop items ("dropped" e.g. and "not dropped").