add Snap a length as a line width

[sb3nder]

Description

Add high level description of the Snap a length as a line width rounding method, to the <length> CSS type" page.

Motivation

The computed value for border-*-width, column-rule-width, outline-width, outline-offset, -webkit-border-*-width, is specified as "the absolute length, snapped as a line width" .
There is no docs explaing what that means, that I can easely link in the computed value description.

Additional details

border-*-width, column-rule-width, outline-width snapped as a line width:
w3c/csswg-drafts#5210

Computed value untangled from *-style properties value:
w3c/csswg-drafts#11494 (comment)

outline-offset snapped as a line width:
w3c/csswg-drafts#12906

Definition of "length snapped as a line width":
https://drafts.csswg.org/css-values-4/#snap-as-a-line-width

Related issues and pull requests

Fixes #44193

Relates mdn/data#1069

[github-actions]

Preview URLs (1 page)

• /en-US/docs/Web/CSS/Reference/Values/length

(comment last updated: 2026-07-08 08:06:55)

[dipikabh]

Hello @sb3nder, thanks for the PR!

Couple of pointers about how we document on MDN:

• We use Markdown style links.
• We don't usually link to the spec in the middle of the prose. Instead, we explain the expected behavior in simple language.
• The algorithm in the spec is for the browser implementers. What we document is how web developers will encounter this behavior.

Hope this helps.

This <length> behavior change could be a single line update - you can consider adding it to the "Syntax" or "Absolute length units" section.
It would also be nice to have a short example to explain this behavior.

[sb3nder]

@dipikabh, thank you for the help.
I gave it another try, let me know what you think.

[dipikabh]

Thanks @sb3nder.

Your update is good; I've proposed some tweaks and also suggested to add it to a different part of the "Syntax" section. Please take a look at my inline suggestions. Thanks!

[dipikabh]

Thanks a lot, @sb3nder!