The in operator allows you to check if a value is present in a set of
values. It can be used with the operator not to check if a value is missing
from a set of values. The set of values is specified as an array.
For example, the following expressions return
true:city = 'Paris', city in ['New York', 'London', 'Paris', 'Tokyo', 'Pekin']
6 not in [1, 2, 3, 4, 5]