Centered/aligned intervals?

interval: 1 or interval: day respectively create [0, 1] and [monday 00:00, monday 23:59:59…] segments, that can be represented as, say, a barX. In some cases we'd prefer the bar to be centered on the value.

This can be done currently with a custom interval: {floor: d => Math.floor(d) - 0.5, offset: (d, n=1) => d + n}, but it could be nice to have a shorthand notation.

maybe intervalAlign: 0.5 (with a default being 0, or 1 depending on the semantics we'd want to give it).

For UTC intervals, we'd have to get a sense of what is an appropriate “day shifted by a fraction”—including when days are 23 or 25 hours-long, or months.

A typical use case: https://talk.observablehq.com/t/observable-plot-cell-and-date-label/8116