The “overflow” is for when people want to book plots for more guests
than is permitted, which the system would need to add a new plot to the
“shopping cart”, as it were; not implemented yet.
The ask zone preferences is to whether show the corresponding input on
the booking form, that it was done implicitly when the campsite type had
options, because up until now it was only for plots, but it is no longer
the case, thus i need to know when to show it; now it is explicit.
