Let user text-spacing overrides work without breakage
Readers change text spacing through a user stylesheet, a bookmarklet, a browser extension or a reading application, and the rule asks that nothing is lost when they do. W3C lists C36 as sufficient for 1.4.12 Text Spacing and puts the obligation plainly. Containers must either already have room for the text to expand, or be able to expand themselves. Its concrete recommendation is one most write-ups miss. Do not set a height on paragraphs. In a language read horizontally the extra spacing makes the paragraph taller, so an unset height lets it grow and a fixed one clips it, and in a vertical writing mode the same argument runs sideways. Where a specific declaration has to be defeated, marking the reader's spacing rules important is the escape, and it is a last resort rather than the plan.
How we find it in an audit
We apply the four spacing values the rule names, line height 1.5, paragraph spacing twice the font size, letter spacing 0.12em and word spacing 0.16em, then read the page. Cut-off text, overlapping blocks and buttons that have burst are the failures. Automated tools flag the fixed heights and only a look tells you which ones lost content.
How affected users experience it
Somebody who has set these values did it because the default made reading hard. If the site breaks when they apply them, they get a choice between text they can read and a page that works, which is not a choice anybody should be offered. A layout that flexes gives them both and costs the site nothing.
Passes vs. fails
Passes
p { line-height: 1.5; }
.summary { min-height: 4em; }Fails
p { line-height: 18px !important; }
.summary { height: 60px; overflow: hidden; }How this gets tested
The W3C publishes test rules that define what a checker looks for here.
- Important letter spacing in style attributes is wide enoughA tool can check this
- Important line height in style attributes is wide enoughA tool can check this
- Important word spacing in style attributes is wide enoughA tool can check this
Other ways to satisfy this rule
6 guides on this site are filed under 1.4.12 Text Spacing. W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
This guide is our interpretation of W3C technique C36: Allowing for text spacing override. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.