Comment by SllX

Also a little extra distinction: “.txt” is a relic of 8.3 DOS filename conventions. He was not bound by these. If you’ve got the space, of course you’ll go with “.text” over “.txt” because text is the input, HTML is the output, Markdown is the tool for converting one into the other, per the first line of the introduction:

> Markdown is a text-to-HTML conversion tool for web writers.

Ergo they’re not Markdown documents, they’re text files that can be converted into HTML using Markdown.

https://daringfireball.net/projects/markdown/