A validator that succeeds only for values that are within (i.e. before or after) a period of the specified
temporal (for example, "within a month of this person's birth date").
This is essentially equivalent to (value >= of - duration) && (value <= of + duration).
(value >= of - duration) && (value <= of + duration)
The desired temporal.
The allowed tolerance.
A textual representation of the specified duration (durations
are rendered to ISO-8601 representations by default, which is likely not the desirable