I'm not convinced about the "edge case" at all. CSS made it an edge case for no reason at all, and made a silly default out of it.

If the box isn't big enough to contain center-aligned text, of course it should spill on both sides, because it's both expected and consistent.

And now the author pretends "we left-align text and spill on the right" as the only possible default behaviour that somehow makes constraints impossible/extremely difficult.

If you don't make assumptions and weird defaults in your system, you don't have to fight them and make weird workarounds.

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pavpanchekha 3 days ago | parent | next [-]

Author here. This specific quirk of CSS is minor, and probably if CSS didn't have this quirk it'd be fine. But I'd guess that you've at least once in your life been on your phone and been browsing a website which used a really long word (or a really long line of code!) in centered text (maybe a heading) and you've scrolled right to read the whole thing. Are you sure your website doesn't have such a thing, if you have centered text somewhere?

So, yes, CSS could have fewer edge cases and workarounds---what I refer to in the post as less implicit knowledge---and then it would be simpler. But the resulting layouts would probably be worse. And a radical simplification like a constraint system would probably be even simpler and the results (I assert) would be even worse. It's fine to want a better life for browser developers, but I don't think it's unthinkable for CSS to create new edge cases and sometimes-surprising behavior if it also results in, typically, better outcomes.

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chrismorgan 6 days ago | parent | prev | next [-]

Layout can only expand/overflow to the right and down, not up or left. Although not fundamental, this has been a standard and useful design limitation in almost all software from the start: infinite drawing canvases are the only counterexample that immediately occurs to me. (“Pull to refresh” is almost another exception.)

I’ve seen sites that centred in a way that caused balanced overflow while assuming a wider viewport than I had. The result was a completely unusable site: the middle half was in-viewport (good), the right quarter was accessible by scrolling (poor), but the left quarter could not be accessed at all (abject failure).

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troupo 6 days ago | parent [-]

> The result was a completely unusable site: the middle half was in-viewport (good), the right quarter was accessible by scrolling (poor), but the left quarter could not be accessed at all (abject failure).

This is the limitation that browsers/css impose for a rather arbutrary reason [1]

There's nothing preventing the browser from scrolling in any direction.

[1] It's not arbitrary, of course. But almost all these quirks stem from the fact that browers were made to display text and images in a single rendering pass. That's why even in 2025 the article talking about constraints talks about these things as self-evident good defaults with no alternatives:

--- start quote ---

If text is centered inside a box too small to contain it, we don't want it spilling out the left edge (it might go off-screen, where the user cannot scroll); left-aligning ensures it only spills out on the right.

That's a funky quirk but also, you may have never noticed it and if you did this edge case probably was better than what the layout would have been. Meaning, actually, building this edge case into the definition of text-align was a smart choice by the CSS designers.

--- end quote ---

It was a smart choice for 1995-1999. It's now codified and cannot be changed, but it doesn't mean it's a good choice now, or that it's even an edge case.

	▲	pavpanchekha 3 days ago \| parent \| next [-]
		Author here. You're right that a lot of CSS's edge cases and implicit rules stem from other choices and implicit rules that maybe need to be reconsidered. But take this logic a step further. The way text with mixed font sizes is laid out is kinda weird—should we just get rid of that? Mixed Chinese-Latin text is weird (search "idiographic baseline"); should we get rid of that? In fact, variable-size characters are weird, maybe just stick to all-Chinese? I'm joking, of course, but my point isn't that a simpler system is inconceivable, just that it would be inconvenient.
	▲	chrismorgan 6 days ago \| parent \| prev [-]
		As I said, it’s not a fundamental limitation, but it is ubiquitous in computing with only a few specialised and obvious exceptions, so breaking it has consequences: you will confuse people. Probably not much, but people don’t try scrolling up from the top of a page, nor left from the left edge. I also expect that from-scratch layout implementations (the theme of the article) would tend to only scroll in the positive direction, because doing otherwise is somewhat painful, and what kind of weird thing would want negative coordinates anyway? —So they would think. This is why the CSS text-align behaviour is surprisingly sane. It solves a subtle problem that you would otherwise expect to encounter.

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rendaw 6 days ago | parent | prev | next [-]

> 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.

	▲	pavpanchekha 3 days ago \| parent [-]
		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.

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bryanrasmussen 6 days ago | parent | prev [-]

>If you don't make assumptions then when edge cases happen that have not been programmed for then the system will probably crash.

>and weird defaults in your system

I'm not sure that there is any sufficiently complex logical system that will never have weird defaults, perhaps caused by the logic of some other seemingly sensible default. Complexity being the root cause of this overarching phenomenon.

	▲	troupo 6 days ago \| parent [-]
		Yes, but you want as few of those as possible. And you don't want to stick to default assumptions from 35+ years ago: https://news.ycombinator.com/item?id=46185345