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[css-values-4] snap a length as a border width: meaning of "Assert: len is non-negative."? #13795
Description
see: https://drafts.csswg.org/css-values-4/#snap-a-length-as-a-border-width
Assert: len is non-negative.
What is the meaning/implication of Assert in this context?
Is the value invalid when negative?
Because step 2 explicitly has "do nothing" I am assuming it makes the value invalid, but this seems weird.
If the intention is to do nothing, it might be better to write as:
1. If len is negative, do nothing.
2. If len is an integer number of device pixels, do nothing.
...
Activity
[-][css-values-4] `snap a length as a border width`: meaning of "Assert: len is non-negative."[/-][+][css-values-4] `snap a length as a border width`: meaning of "Assert: len is non-negative."?[/+]Loirooriol commentedon Apr 12, 2026
It means that whatever invokes the "snap a length as a border width" algorithm should make sure that
lenis non-negative.romainmenke commentedon Apr 12, 2026
Thanks!
In that case this is somewhat related to: #13794
This can indeed be read as an assert that A must be positive and that in other cases there is no snapping to border width.
fantasai commentedon May 8, 2026
... This doesn't seem great? It should snap a negative number
snap(N)same as-snap(|N|).fantasai commentedon May 8, 2026
Fixed in c196082
@romainmenke @Loirooriol Please re-open if there's a problem remaining, but we think this handles it.