import { PropertyValues } from 'lit';
import { SpectrumElement } from '../../element/index.js';
/**
 * Base class for a tab panel that displays content associated with
 * a tab.
 *
 * Manages visibility, ARIA hidden state, tabindex, and the
 * focus-in/out behavior that prevents Tab-key trapping inside panel
 * content.
 *
 * In 1st-gen, `slot="tab-panel"` was
 * assigned programmatically in `firstUpdated` so consumers never
 * wrote it in markup. This behavior is preserved in 2nd-gen.
 *
 * The panel removes its own
 * `tabindex` on `focusin` so that Tab presses inside the panel
 * move to the next interactive element rather than being trapped.
 * On `focusout`, `tabindex` is restored so the panel remains
 * focusable from the tablist.
 *
 * @slot - Content displayed when the associated tab is selected
 */
export declare abstract class TabPanelBase extends SpectrumElement {
    /**
     * Whether this panel is currently visible (its associated tab is
     * selected). Managed by the parent `swc-tabs` — consumers should
     * not set this directly.
     */
    selected: boolean;
    /**
     * Unique identifier linking this panel to its corresponding tab.
     * Must match the `tab-id` attribute on the associated `swc-tab`.
     */
    tabId: string;
    /**
     * Removes the panel's `tabindex` while focus is inside the panel
     * so that Tab presses navigate to the next interactive element
     * rather than the panel container itself.
     */
    protected handleFocusin(): void;
    /**
     * Restores `tabindex` when focus leaves the panel so the panel
     * remains directly focusable from the tablist via Tab key.
     */
    protected handleFocusout(): void;
    protected firstUpdated(_changes: PropertyValues): void;
    protected updated(changes: PropertyValues): void;
    private syncVisibility;
}