org-mode code fence for markdown

[Norwid Behrnd <nbehrnd@yahoo.com>]

Dear list,

based on previous experience to fence small snippets of code in org-mode e.g.,
for Fortran in a pattern like

```org
* example Fortran (not FORTRAN 77)

  #+begin_src f90 :tangle echo.f90
program test
  implicit none
  write (*, '(A)') "Fortran"
end program test  
  #+end_src
```

I seek a similar fence to document a pattern in Markdown.  An example would be
a nested list such as 

```markdown
* Item 1
* Item 2
  - Item 2a
    + Item 2a1
  - Item 2b
* Item 3
```

Contrasting to my anticipation, neither `C-c C-, s` followed by a tentative
«md», nor «markdown» yield a box which opens by `C-c '`.  Neither table 1, nor
2 on worg's documentation[1] mentions markdown.

Is there a special key (similar to f90 for contemporary Fortran) /to tangle/
selected, individually fenced snippets of .md stored in one .org file into one
.md file which wasn't yet added to these tables?  Or -- given subtle
differences in the dialects e.g., by Gruber, GitHub, Pandoc -- is there too
little benefit for such an additional bridge, perhaps especially whole .org
documents may be rewritten into any of the three forms of .md by pandoc, and
`C-c C-e` equally may be configured to export a buffer of running Emacs
org-mode to .md?

Norwid

[1] https://orgmode.org/worg/org-contrib/babel/languages/index.html