Markdown that does not appear in the reply box:

Strikethrough:

some ~~strikethrough~~ text

some ~~strikethrough~~ text

Horizontal Rule:

***

Table with alignment:

||X|Y|Z|
|--------|:---|:----:|---:|
|1|X1|Y1|Z1|
|2|X2|Y2|Z2|

Codeblock:

`**codeblock**`  
`enclose in 3 backticks`  

**codeblock**
enclose in 3 backticks

   **codeblock**
   indent with 4 spaces

**codeblock**
indent with 4 spaces

Heading 1:

# heading 1

heading 1

Heading 2:

## heading 2

heading 2

(Heading 3 you get when you press the H button in the reply box)

Markdown that kbin does not yet support but lemmy does:

Spoilers:

hidden or nsfw

spoilers here

Superscript:

some ^superscript^ text

some ^superscript^ text

None amongst kbin, lemmy and reddit support subscript as far as I can tell.

What this page looks like in kbin
What this page looks like in lemmy

More info:
https://commonmark.org/help/
https://spec.commonmark.org/dingus/

https://join-lemmy.org/docs/en/users/02-media.html
https://calckey.social/mfm-cheat-sheet