Function required

Requires a value to be present.

Rejects undefined outright, delegating anything else to the wrapped validator, so a mandatory property is reported as missing rather than passing unchecked.

This is the only constraint that reports an absent value as missing: the value-domain validators assume a value to inspect, and a type guard hands a missing one to its unknown branch, which reports it as a type mismatch rather than as absent. Wrap the value-domain constraints of a mandatory property in this check to have absence reported.