readableWidth

Caps a prose column at a comfortable measure and centres it.

The failure this prevents is invisible on a phone and unmissable on a desktop: text stretched the full width of a 2560dp window runs past 200 characters a line, and the eye loses its place on the return sweep. Typographic guidance puts the comfortable measure at 45–75 characters.

The cap is per-surface rather than one constant, because the character count is what matters and the type scale differs: a television sets body text at 18–22sp, so the same number of characters needs materially more dp than it does at 14sp on a phone. A watch is never capped — the screen is already narrower than any sensible measure.

Use this for paragraphs, articles, changelogs, MarkdownText. Use contentWidth for dashboards and card grids, which read fine much wider.