Are Gantt chart milestones supposed to work like this?

[fuzyll]

Here's an example Gantt chart:

gantt
  title Milestone Test
  section Milestones
    Milestone 1 : milestone, m1, 2023-09-18, 7d
    Milestone 2 : milestone, m2, after m1, 28d
    Milestone 3 : milestone, m3, after m2, 7d
  section Tasks
    Task 1 : a1, 2023-09-18, 7d
    Task 2 : a2, after a1, 28d
    Task 3 : after a2, 7d

This renders like this in Mermaid Live:

Is that...intended? My understanding of a milestone is that it's marking the date by which something is supposed to be reached (done, whatever). I would either expect to not have the 4th argument at all (e.g. i specify the exact date upon which something is done), or to have the 4th argument push the milestone out that many days. Instead, it centers the milestone over that period.

The only way to get the behavior I want out of this seems to be milestone, tag, exact date, 0d. This basically approximates not having the 4th argument at all. Unfortunately, it means I can't use the after tag syntax at all, unless I want to do silly stuff like find the thing I want and multiply by 2 to get it centered on the place I want.

This is sort of explained in the docs, but poorly, and I don't understand why it's implemented this way. Is anyone able to clue me in on what I'm missing?