/**
 * Estimate the reading time, taking readability of the document and a target
 * age group into account.
 *
 * For some more background info/history and a few insight on where this all
 * comes from, see: <https://martech.org/estimated-reading-times-increase-engagement/>.
 *
 * ###### Algorithm
 *
 * The algorithm works as follows:
 *
 * *   estimate the WPM (words per minute) of the audience age based on the facts
 *     that English can be read at ±228 WPM (Trauzettel-Klosinski), and that
 *     reading rate increases 14 WPM per grade (Carver)
 * *   apply the readability algorithms Dale—Chall, Automated Readability,
 *     Coleman-Liau, Flesch, Gunning-Fog, SMOG, and Spache
 * *   adjust the WPM of the audience for whether the readability algorithms
 *     estimate its above or below their level
 * *   `wordCount / adjustedWpm = readingTime`
 *
 * > ⚠️ **Important**: this algorithm is specific to English.
 *
 * @param {Nodes} tree
 *   Tree to inspect.
 * @param {Readonly<Options> | null | undefined} [options]
 *   Configuration (optional).
 * @returns {number}
 *   Estimated reading time in minutes.
 *
 *   The result is not rounded so it’s possible to retrieve estimated seconds
 *   from it.
 */
export function readingTime(tree: Nodes, options?: Readonly<Options> | null | undefined): number;
export type Nodes = import('hast').Nodes;
/**
 * Configuration
 */
export type Options = {
    /**
     * Target age group (default: `16`).
     *
     * This is the age your target audience was still in school.
     * Set it to 18 if you expect all readers to have finished high school,
     * 21 if you expect your readers to all be college graduates, etc.
     */
    age?: number | null | undefined;
};