HN doesn't use markdown:
https://news.ycombinator.com/formatdoc
I use markdown on HN, partially out of protest, partially because it looks fine enough when rendered as plain text (by design).
Re:Advice to Young Web Developers
by fluffycritter on Thursday June 18, 2020 @08:31PM
(#23569726)
Ah, thanks, force of habit. :)
EDIT: I've updated the Tumblr version to make this a bit more clear.