Font loading and performance

Webfonts are render-blocking-adjacent resources that change text metrics when they arrive. Two separate problems: when text becomes visible, and whether the page moves when the font swaps.

⚠️ Part of the corpus is obsolete here — but not all of it. Rutter (2017) calls font-display "a nascent CSS property under development," supported only behind experimental flags at the time; that support status is obsolete — font-display now has universal support and is the standard mechanism. His five-value taxonomy and their descriptions (auto/block/swap/fallback/ optional), however, match the current spec closely and are still accurate — don't discard the substance along with the outdated adoption note. What's genuinely dead is the workaround the books reach for instead: the Font Loading API + wf-loading/wf-active/wf-inactive classes (Rutter) and Web Font Loader (both Rutter and Santa Maria) exist specifically to fake font-display behavior in browsers that don't support it. No browser needs that workaround now. Source-hierarchy rule 1 (browser behavior) outranks rules 4 and 8. Verify against MDN before emitting code.