export interface FontGenerations {
    /** The shorthand to set on a canvas for `font`: `font` itself until a
     *  face of one of its families arrived late, then the same with that
     *  family named once more per generation. Notes that the families of
     *  `font` have been measured with. */
    resolve(font: string): string;
    /** Faces of `families` arrived or left. The ones a shorthand was already
     *  set for move to their next generation, so the next `resolve` of a
     *  shorthand that names them gives one the canvas has not seen. Returns
     *  those families (in lower case). */
    changed(families: Iterable<string>): string[];
}
export declare function createFontGenerations(): FontGenerations;
/** A 2D context class whose `font` the generations stand in front of. */
interface ContextClass {
    prototype: object;
}
/**
 * Put `generations` in front of every `font` set on a canvas of this
 * worker: the engine's measuring context, the ones the marks are measured
 * on, and the text library's own, which the engine cannot hand a context
 * to. `contexts` are the classes to cover (by default the worker's
 * `OffscreenCanvasRenderingContext2D`). Returns how many were covered: 0
 * where there is no such class or its `font` cannot be redefined, and the
 * worker then measures as before.
 */
export declare function installFontGenerations(generations: FontGenerations, contexts?: readonly (ContextClass | undefined)[]): number;
export {};
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