/**
 * Font optimization helpers.
 *
 * Three concerns:
 *   1. `buildFontPreloadLink`  — `<link rel="preload" as="font" crossorigin>` descriptor
 *      for a self-hosted font file. Caller renders the JSX/HTML.
 *   2. `buildFontFaceCss`      — emits `@font-face` blocks with `font-display: swap`
 *      so the browser shows fallback glyphs instead of an invisible flash.
 *   3. `googleFontsUrl`        — composes a Google Fonts CSS2 URL with weight axes
 *      and `display=swap`, plus its preconnect link pair.
 *
 * All helpers are pure-data; no DOM access, no fetch, safe in workers.
 */
export type FontFormat = 'woff2' | 'woff' | 'ttf' | 'otf';
export interface FontFaceDescriptor {
    family: string;
    src: string;
    /** File format (used for `format()` hint + preload `type`). */
    format?: FontFormat;
    weight?: number | string;
    style?: 'normal' | 'italic' | 'oblique';
    /** `font-display`. Default: `swap` — prevents FOIT (flash of invisible text). */
    display?: 'auto' | 'block' | 'swap' | 'fallback' | 'optional';
    /** Unicode range to subset the font (e.g. `U+0000-00FF` for latin-1). */
    unicodeRange?: string;
}
export interface FontPreloadLink {
    rel: 'preload';
    as: 'font';
    href: string;
    type: string;
    crossorigin: 'anonymous';
    fetchpriority?: 'high' | 'low';
}
export declare function buildFontPreloadLink(src: string, format?: FontFormat, opts?: {
    fetchPriority?: 'high' | 'low';
}): FontPreloadLink;
export declare function buildFontFaceCss(descriptors: FontFaceDescriptor[]): string;
export interface GoogleFontFamily {
    family: string;
    /** Weight axes — single number or array of weights. */
    weights?: Array<number | {
        italic: boolean;
        weight: number;
    }>;
}
export interface GoogleFontsUrlOptions {
    families: GoogleFontFamily[];
    display?: FontFaceDescriptor['display'];
    /** Subset (e.g. `latin`, `latin-ext`). */
    subset?: string;
    /** Override the base URL — test hook. */
    baseUrl?: string;
}
export declare function googleFontsUrl(opts: GoogleFontsUrlOptions): string;
/**
 * Preconnect to Google's font hosts. Two links: the CSS host + the static
 * file host (separate origin so two TLS warmups beat any latency hides).
 */
export declare function googleFontsPreconnectLinks(): Array<{
    rel: 'preconnect';
    href: string;
    crossorigin?: 'anonymous';
}>;
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