import { type TreeElement } from "../util/element.js";
/**
 * Base class for an extractor that converts input into a tree element.
 * - Extractors are composable: outer extractors delegate to inner extractors.
 * - The output type is always a `TreeElement` (or a more specific subtype).
 */
export declare abstract class Extractor<I, O extends TreeElement = TreeElement> {
    /** Extract a tree element from the given input. */
    abstract extract(input: I): O | Promise<O>;
}
/**
 * Merge two tree elements — `primary` keeps its identity (`type`, `key`, `source`); `secondary` contributes any
 * metadata `primary` does not already have.
 * - `title` and `description` are taken from `primary` when set, otherwise from `secondary` — primary stays canonical
 *   but a missing field falls back rather than disappearing.
 * - `content` and `children` from both are concatenated (primary first).
 */
export declare function mergeTreeElements<T extends TreeElement>(primary: T, secondary: TreeElement): T;