OS/2 vs hhea ascender mismatch

Definition

OS/2 typoAscender doesn't match hhea ascender. The two values should be equal — line-height computations on Mac/iOS read OS/2, on Windows browsers read hhea, and a mismatch causes line spacing to differ across platforms.

How Patens surfaces this

The Patens audit module checks for metrics-asc-mismatch across five teaching surfaces: the edit-panel inline issue list, the project-wide audit page, the release pre-flight check, the family hub, and the home-page project tile. Every surface shows the same plain-English explanation and links back to this page. This rule is detection-only — there's no automatic fix because the correction is design-dependent (it requires a judgment call about the glyph's intended shape or the font's intended behaviour). The audit message links to the specific glyph or field that needs attention.

Run this check yourself

Patens runs every audit rule live as you draw — including this one. The editor (in private alpha) shows metrics-asc-mismatch firing on real glyphs, or check your own work from the CLI:

npx patens audit your-project.font.json

Related rules in Vertical metrics

• metrics-cap-above-ascender Cap-height above ascender
• metrics-desc-mismatch OS/2 vs hhea descender mismatch
• metrics-descender-nonnegative Descender is non-negative
• metrics-gap-mismatch OS/2 vs hhea line-gap mismatch
• metrics-use-typo-off USE_TYPO_METRICS flag off
• metrics-win-clip-bottom winDescent below typoDescender (bottom clip risk)
• metrics-win-clip-top winAscent below typoAscender (top clip risk)
• metrics-x-above-cap x-height above cap-height
• metrics-zero-height Cap or x-height is zero