Only the doctype, title, and the loss of </link>, are required for it to validate as HTML5; <head> and <body> are implied.
I think the original `markdown` utility generated a HTML fragment rather than a standalone page. If so, perhaps the point of this is that adding the CSS link is the Simplest Thing That Can Possibly Work in order to improve the page appearance?
I think the original `markdown` utility generated a HTML fragment rather than a standalone page. If so, perhaps the point of this is that adding the CSS link is the Simplest Thing That Can Possibly Work in order to improve the page appearance?