font-loading-and-performancelisted

# 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**. ⚠️ **The corpus is obsolete here.** Rutter (2017) describes `font-display` as "a nascent CSS property under development" and both Rutter and Santa Maria recommend Web Font Loader. Superseded. Source-hierarchy rule 1 (browser behavior) outranks rules 4 and 8. Verify against MDN before emitting code. ## 1. When to invoke - Adding, replacing, or auditing webfonts. - FOIT (invisible text) or FOUT (unstyled flash) reported. - CLS regression traced to text. - Font payload is large, or you're choosing between static and variable files. - Self-hosting vs. a font CDN. ## 2. Required context - Which **families, weights, styles, and scripts** are genuinely used. Most sites ship far more than they render. - Whether the font is **self-hosted or third-party**. - Whether the text is **above the fold**. - The **fallback stack** and how far its metrics sit from the webfont. - Current **CLS** and whether font swap contributes. - Whether a **variable font** could replace multiple static files. ## 3. Invariant principles - **Text must never be invisible indefinitely.** A font that fails to load must not take the content with it. - **Only ship glyphs you render.** Unused weights, styles, and language ranges are pure cost. - **WOFF2 is the format.** Universall