(I personally use “.text” for my own files, and have BBEdit set to use Markdown syntax coloring for that extension, which is why I never saw a need to endorse an official extension.)"
https://daringfireball.net/linked/2014/01/08/markdown-extens...
It is my assumption that Gruber chose ‘.text’ over ‘.txt’ for several reasons. To give it a little difference when searching for files. To be more legible to non-computer people. And finally, while Classic MacOS did not use file extensions, the Resource Fork type code for text files was ‘TEXT’
> 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.