I'm curious about how this is legal in the EU. Is this because regions like the Basque have that autonomy financially? This kind of thing is not an option in th

I'm curious about how this is legal in the EU. Is this because regions like the Basque have that autonomy financially? This kind of thing is not an option in the US, right? Is there a good write up anywhere that specifies when and where this kind of thing could happen?