/**
 * A Set-like class that manages custom states for DOM elements.
 * Extends the native Set to provide state management functionality
 * that can work with either DOM attributes or an existing Set.
 */
export declare class StateSet extends Set<string> {
    private _el;
    private _existing;
    /**
     * Creates a new StateSet instance.
     * @param el - The DOM element to manage states for
     * @param existing - An optional existing Set to use for state storage
     */
    constructor(el: Element, existing?: Set<string> | null);
    /**
     * Adds a state to the set and applies it to the element or existing set.
     * @param state - The state name to add
     * @returns The StateSet instance for method chaining
     */
    add(state: string): this;
    /**
     * Removes a state from the set and from the element or existing set.
     * @param state - The state name to remove
     * @returns Always returns true (for Set compatibility)
     */
    delete(state: string): boolean;
    /**
     * Checks if a state exists in the set.
     * @param state - The state name to check
     * @returns True if the state exists, false otherwise
     */
    has(state: string): boolean;
    /**
     * Removes all states from the set and from the element or existing set.
     */
    clear(): void;
}