But author is not writing plain text files. As he shows at the end he is clearly writing some mixture of HTML and some custom language that he uses to parse title, tags, and date. I do agree that unless absolutely needed you shouldn't tie yourself to proprietary formats, but unless you are writing simple notes you probably want more functionality out of your files than actual plain text file can provide at which poin…
Code I write, be it python, php, HTML or JS is still plain text as a format. I can open any of these code documents in any dumb text editor. The fact that some other tool can do more with these files, parse them, execute them, "extract" some logic from them isn't relevant to the fact that I can open, read and edit these files as a pure and plain text file. Therefore adding parsable parts/logic to files like YAML head…
Just use the good old file program and you'll see that in any coherent world we classify python, php, html, and js files as different from actual plain text files.
This very much feels like you are trying to argue tea is same as plain water.