Important! Again, I reiterate, because this is important! This is the original Markdown documentation and reference, which is still pretty good for modern use.
20180516/https://daringfireball.net/projects/markdown/syntax
Now what about that Daring Fireball website? It has a blog of its own written in Markdown, correct? Indeed, this is the case.
20180516/https://daringfireball.net/
Very interesting news here. Twitter is removing support for third party clients. Looks like Twitter is on the fall.
20180516/https://daringfireball.net/2018/05/the_end_of_third_party_twitter_clients