A region representing an interval on one or more axes of a Frame

The Interval class implements a Region which represents upper and/or
lower limits on one or more axes of a Frame. For a point to be within the region
represented by the Interval, the point must satisfy all the restrictions placed on all
the axes. The point is outside the region if it fails to satisfy any one of the
restrictions. Each axis may have either an upper limit, a lower limit, both or neither.
If both limits are supplied but are in reverse order (so that the lower limit is
greater than the upper limit), then the interval is an excluded interval, rather than
an included interval.

Note, The Interval class makes no allowances for cyclic nature of some coordinate systems (such as SkyFrame coordinates). A Box should usually be used in these cases since this requires the user to think about suitable upper and lower limits,

The Interval class inherits from the
Region class.

The Interval class does not define any new attributes
beyond those which are applicable to all Regions.

The Interval class
does not define any new functions beyond those which are applicable to all Regions.

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