Extended intervals?

[Fil]

A technique demonstrated here to extend an interval’s range from the day before the first day to the day after the last, allowing to create a "complete" area. I come across this frustrating situation once in a while, and wonder if we could have a built-in option for this. Maybe Plot.extendInterval("day")? Or, we don't, but it would be nice instead to expose Plot.interval with an argument such as "3 days" or 1, that returns an object with {floor, offset, range}, so we can tweak that programmatically?