How prevent canvas.pointerDrag falling through to splitview

I have a canvas that a user can drag over to select different items. Unfortunately if this canvas is placed on a splitView , a sideways drag brings up the MasterView. I see there is an EventInfo associated with the pointerDrag and a “handled” property which sounds promising - but it is undocumented.

I’m looking for the equivalent of the return true in desktop mouse events, but I guess its different in the asynch world of iOS.