Function sequence

docs/app/js/sanddance-app.js:111386–111388

(ival, start, stop, step)

    return offset(utcInterval(unit), date, step);
}
function sequence(ival, start, stop, step) {
    return ival ? ival.range(start, stop, step) : undefined;
}
function timeSequence(unit, start, stop, step) {
    return sequence(timeInterval(unit), start, stop, step);
}