Intervals

Work with date/time ranges in GMT.

• Interval Basics — validate intervals, construct them from a point plus duration, and understand the two API shapes.
• Containment and Overlap — test whether a point or interval is contained and compute intersections.
• Set Operations — union, difference, xor, merge, and symmetric-difference over intervals.
• Splitting and Counting — split intervals by duration unit, count calendar-unit boundaries, and measure fractional length.