Thoughts on the movable rear wing

[englishpremier]

Just read this on the moveable rear wing...

Next season the F-duct will be outlawed and instead all cars will feature a rear wing flap that can only be used when the driver remains a certain distance behind the car he is chasing. When activated, the flap will replicate the F-duct's effect of reducing drag, in theory making overtaking much easier as the driver ahead cannot deploy the wing in defence.

I don't understand the bit about the driver in front not being able to deploy his in defence...how will that work is it electronically monitored who pressed theirs first, or is it just open to interpretation.

What if the driver in front is at a point where he would normally use the device but someone behind him decides to use it?

It's not very clear

 

[englishpremier]

So, the first question that comes to mind is: could the lead car deploy his flap if approaching a backmarker?

if not, what if a backmarker delpoys his flap?