Daring Fireball had the ‘.text’ version since at least the public release of Markdown, if not earlier.

This should be the version Gruber edits in MarsEdit or BBEdit, but it maybe partly rendered by the Moveable Type CMS

The extension is ‘.text’ because that is what he suggested as the Markdown extension, but of course most of us went with ‘.md’

While keyword tags are not used on the website, you can see the one he uses for his personal purposes at the bottom of the Markdown