[csswg-drafts] [css-values-4] Agressively simplifying a Sum node can change the sign of 0 (#13919)

cdoublev has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-values-4] Agressively simplifying a Sum node can change the sign of 0 ==
#13069 added the simplification of Sum nodes containing an unresolved value and negate nodes. For example, `1px - (1em + 1px)` is simplified to `1em`.

But this simplification can change the sign of zero, like in `order: sign((-1 * 0px) - (1em - 1em))`. If I am not mistaken, with the new simplification requirement, it simplifies to `sign(-0px + -1em + 1em)`, which resolves to `sign(-0px - 1px + 1px)` assuming `1em` resolves to `1px`.

Note that signed zeros cannot be written in CSS. At least, they are not supposed to.

Also note that [ordering calculation terms](https://drafts.csswg.org/css-values-4/#sort-a-calculations-children) can have a similar effect.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13919 using your GitHub account


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Received on Wednesday, 13 May 2026 03:57:03 UTC