I'm not sure why it's called destination/source for mask, maybe a placeholder, cause it means something different like intuitively you would expect.Mask defines how a given bandwith will affect clients and not their direction.Destination means share the total bandwidth of this pipe among all connected clients.Source means provide all connected clients up to a maximum of this pipe configured bandwidth
No, just check the updated help texts for masks in pipe and queue, they are explaining it very well.