import { type FontFaceSetLike } from './faces.js';
/** Whether the engine has looked at `fontSet` before. */
export declare function isFontSetTracked(fontSet: FontFaceSetLike): boolean;
/**
 * Look at `fontSet` again: the families whose loaded faces changed since
 * the last look get their measurements dropped (`evictFontFamilies`) and
 * are returned. The first look only records the set. Cheap when nothing
 * happened: the set is walked only when its size changed, while it is
 * loading, or once a face finished loading. `evict: false` records the
 * set without dropping anything (the caller drops what it knows changed).
 * `force: true` walks it whatever it reports: for a caller that has just
 * awaited `fontSet.load`, whose `loadingdone` is still to come.
 */
export declare function syncFontSet(fontSet?: FontFaceSetLike | null | undefined, options?: {
    evict?: boolean;
    force?: boolean;
}): string[];
/** Told which families' faces changed (lower case). */
export type FontsChangedListener = (families: readonly string[]) => void;
/**
 * Call `listener` whenever faces of a watched font set arrive or leave
 * (see {@link watchFonts}), after the engine has dropped what it measured
 * in their families: the host lays out again. Returns the unsubscribe.
 */
export declare function onFontsChanged(listener: FontsChangedListener): () => void;
/**
 * Watch `fontSet` (by default `document.fonts`, or `self.fonts` in a
 * worker): when faces finish loading, the measurements of their families
 * are dropped — at most once per animation frame, however many slices a
 * burst brings — and the {@link onFontsChanged} listeners are told.
 * Calls nest; the returned function stops this watch. `prepareFonts`
 * starts one on the set it loads into.
 */
export declare function watchFonts(fontSet?: FontFaceSetLike | null | undefined): () => void;
/** Whether `fontSet` is watched. */
export declare function isWatchingFonts(fontSet?: FontFaceSetLike | null | undefined): boolean;
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