Those who run a shop can open it for business, or close it, with
SHOP OPEN and SHOP CLOSE - so a shopkeeper can choose to trade
only while they are there to mind the counter. Nothing can be bought
from, or sold to, a closed shop, though passersby may still browse its
wares through the window. A shop is open unless it has been closed.
This works from either the shop's public storefront or its stockroom,
for its owner or renter, those who run it on an organisation's behalf,
and, for a settlement's own shops, its officials.
Caravans are opened and closed with CARAVAN OPEN and CARAVAN
CLOSE instead.
Syntax:SHOP OPENSHOP CLOSE