alt Hacker News> designers are, by necessity, going to rely on implicit knowledge encoded somewhere on what to do in edge cases
This seems to be implying that designers rely on quirks like the left alignment thing and not behave consistently... that seems like a crazy assertion to me.
And that appears to be the crux of the argument. A more general, consistent system wouldn't provide enough context for the browser to provide specific quirks, so instead a system with a different parameter for every single individual use case where quirks can be introduced to parameters individually is better.
Author here. I suppose it depends on what "rely on" means, but... have you ever used CSS to center text? Did you think much at all about what happens if the zoom level is high enough and the screen size small enough that the text doesn't fit? I assume not (I don't think I'd ever thought about that before I read that part of the standard), so in that sense you were relying on this behavior. I do think that in most cases where it activates, the quirk implemented by CSS probably improves the layout.