Ability to show the TOC both in body and right simulataneously

[dragonstyle]

Discussed in #3336

^{Originally posted by AlFontal November 15, 2022}
As far as I know, it's possible to select a single location to show the Table of Contents, but while the dynamic TOC that always stays on the right is useful, sometimes I also want to show a full TOC just after the header in an article/blog post.

Is there any mechanism to have it behave like that right now?

One way we could think about approaching this could be to make the toc-location parameter optionally a list.

It can support

format:
  html:
    toc: true
    toc-location: body

as it does today.

It could then additionally support

format:
  html:
    toc: true
    toc-location:
      - left
      - body

---

Another approach which is a bit more quick-and-dirty, would be to add the additional two options left-body and right-body. This would keep it a single value and prevent the support of the likely unwanted right and left.

[dragonstyle]

This seems like a good way to accomplish this. I think that supporting both left and right simultaneously is going to be a little annoying to implement because our grid system has some special accommodations for toc: left and I'm not completely sure how that grid will work with elements in both the left and right margins (it might be ok, but not sure).

It doesn’t seem that there is a need currently for both right and left just body and one of the sides.
Another approach could be right-body left-body that captures both locations as a single value.

It isn't super clean, although we wouldn’t be implementing features that folks likely wouldn't want.