import type { IButton, IContextualMenuProps } from '@fluentui/react';
import type React from 'react';
/**
 * Returns a ref that populates both the internal mutable ref and an optional external ref.
 * Handles both callback refs and RefObject externals.
 *
 * @param internalRef - Component-owned mutable ref used for internal logic (e.g. opening a menu).
 * @param externalRef - Caller-supplied ref, if any.
 * @returns A merged React.Ref that satisfies both.
 */
export declare function mergeButtonRef<T>(internalRef: React.MutableRefObject<T | null>, externalRef: React.Ref<T> | undefined): React.Ref<T>;
/**
 * Shared keydown handler for buttons with a contextual menu.
 * Intercepts Alt+Down before Fluent's _onMenuKeyDown runs: calling preventDefault()
 * sets ev.defaultPrevented=true, which causes Fluent to skip its own stopPropagation().
 * The Down keydown then bubbles up, preventing the host application's menubar from
 * stealing focus after the menu is dismissed.
 * No-ops when menuProps is absent — Alt+Down is only intercepted when a menu is present.
 *
 * @param ev - The React keyboard event from the button's onKeyDown handler.
 * @param buttonRef - Ref to the Fluent IButton instance used to programmatically open the menu.
 * @param onKeyDown - Optional caller-supplied onKeyDown handler, forwarded after internal handling.
 * @param menuProps - Menu configuration; Alt+Down is only intercepted when this is defined.
 */
export declare function handleMenuKeyDown(ev: React.KeyboardEvent<any>, buttonRef: React.RefObject<IButton>, onKeyDown?: (ev: React.KeyboardEvent<any>) => void, menuProps?: IContextualMenuProps): void;
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