Potential Coal price cap and impact on TER, page-6

I'm just totally confused how this cap would even work.
they say, ok, we are capping domestic sales of coal.
suddenly, no companies will want to sell coal domestically, and they will go looking for offshore buyers.. which will cause the cost of coal and power generation in this country to skyrocket!?
or, they come out and say, ok we are capping all coal sales out of this country.. how does that even work into an international market?
China would fall over laughing at us if we said to them.. Hey you can have your coal at half price from now on!
if anyone can outline a scenario where either of these ideas could work i would love to hear it.
The whole thing sounds like the dumbest idea ever.