Re: [csswg-drafts] [css-borders] Add a 'hairline' border-width value (#3720)

The CSS Working Group just discussed `[css-borders] Add a 'hairline' border-width value`.

<details><summary>The full IRC log of that discussion</summary>
&lt;fantasai> TabAtkins: Discussed border-rounding behavior, where borders with nonzero width but less than a pixel will round to something visible<br>
&lt;fantasai> TabAtkins: lot of discussion<br>
&lt;fantasai> TabAtkins: conversation seemed to lean towards exposing a 'hairline' keyword for a few propoerties<br>
&lt;fantasai> TabAtkins: and maybe a rounding function that rounds like borders do, always away from zero<br>
&lt;fantasai> TabAtkins: since then, Oriol suggested 'hairline' as a unit<br>
&lt;fantasai> TabAtkins: maps to a number of device pixels<br>
&lt;fantasai> TabAtkins: can be used as a length unit anywhere lenghts are allowed<br>
&lt;fantasai> TabAtkins: avoids need for new rounding function<br>
&lt;fantasai> TabAtkins: also useful if you want another box to match the width of a box with hairline border<br>
&lt;fantasai> TabAtkins: could specify calc(100px + 2hairline)<br>
&lt;fantasai> TabAtkins: smfr concerned that larger multiples wouldn't be reasonable<br>
&lt;fantasai> TabAtkins: but use cases for small multiples<br>
&lt;emilio> q+<br>
&lt;fantasai> TabAtkins: so I suggest resolving on this approach<br>
&lt;fantasai> TabAtkins: a new unit that is 1px or less, but at least one device pixel<br>
&lt;Rossen5> ack emilio<br>
&lt;smfr> q+<br>
&lt;TabAtkins> emilio: one question, should we make it a keyword rather than a unit?<br>
&lt;TabAtkins> emilio: a unit that's such a mouthfull feels weird<br>
&lt;emeyer> q+<br>
&lt;flackr> q+<br>
&lt;dandclark> TabAtkins: A keyword either is not usable in calc, or is one of hte calc keywords, unless we do something to make it usable both ways<br>
&lt;TabAtkins> smfr: i wo9uldn't object to the unit, think ti's a bit weird tho<br>
&lt;dandclark> TabAtkins: Exactly what we do today with border witdths less than a pixel. We still have some def of what it means internally<br>
&lt;emeyer> q-<br>
&lt;TabAtkins> fantasai: i think making this a unit feels wrong, if you want the boxes to match you should use box-sizing<br>
&lt;Rossen5> ack smfr<br>
&lt;Rossen5> ack fantasai<br>
&lt;jfkthame> fantasai++<br>
&lt;TabAtkins> fantasai: people might start using the unit to reference device pixels in a way that's more fragile than we want<br>
&lt;TabAtkins> flackr: if an author wants something thicker than a hairline...?<br>
&lt;TabAtkins> TabAtkins: max(1hairline, .3px)<br>
&lt;Rossen5> ack flackr<br>
&lt;Rossen5> ack fantasai<br>
&lt;TabAtkins> fantasai: i think ahving a rounding function makes more sense<br>
&lt;emilio> fwiw, I think implementing it as a keyword seems trivial-ish as well (so that it works in calc() and other &lt;length>s too)<br>
&lt;TabAtkins> TabAtkins: well this clearly wasn't doable in five minutes<br>
&lt;emeyer> I have concerns about device printing with a unit that yields a number of device pixels.<br>
&lt;emeyer> s/printing/fingerprinting/<br>
&lt;TabAtkins> emeyer, device pixel ratio is already exposed in numerous other ways<br>
</details>


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Received on Wednesday, 7 May 2025 17:02:12 UTC