Finding out whether . is contained in a given array or not, evidently. (That's not strictly true - you can do it, you just have to bend over backwards for what

Finding out whether . is contained in a given array or not, evidently. (That's not strictly true - you can do it, you just have to bend over backwards for what is essentially the "in" keyword in python, sql, etc. jq has no less than four functions that look like they should do that - in(), has(), contains() and inside(), yet they all do something slightly different)