[so] in a comment, it expands to "Stack Overflow" with a link. I used this in a citation,
like [so], to abbreviate the citation. Luckily, you guys are great and allow it to be escaped (I was afraid this custom expansion thingy might not be part of the markdown and might not be escapeable) by placing a backslash in front of it,
like \[so]. However, this comment was later moved to chat, and there we can now see the Stack Overflow link.