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

External URLs (1)

URL: /en-US/docs/Web/CSS/Reference/Values/length
Title: <length> CSS type

• https://drafts.csswg.org/css-values/ (1 time) (Note! This may be a new URL 👀)