/**
 * Custom property carrying the shared alert flash phase, ramping 0 → 1 → 0.
 *
 * Alerting surfaces sample this rather than running animations of their own, because independent
 * CSS animations start whenever their element started and drift apart. Registered as an
 * inheritable `<number>` on the document, so it reaches into shadow trees — a grid row deep inside
 * a component's shadow DOM stays in step with a tab header in the light DOM.
 *
 * @public
 */
export declare const alertFlashPhaseProperty = "--alert-flash-t";
/**
 * Custom property setting how long one flash cycle takes. Set it on `:root` to retime every
 * alerting surface at once.
 *
 * @public
 */
export declare const alertFlashDurationProperty = "--alert-flash-duration";
/**
 * Starts the document-level clock that alert flashes sample.
 *
 * Safe to call repeatedly and from any number of components — the first call does the work. Called
 * automatically by the components that flash, so apps only need this to start the clock earlier.
 *
 * Does nothing where `CSS.registerProperty` or constructable stylesheets are unavailable, which
 * leaves alerting surfaces on their static fallback colour rather than breaking them.
 *
 * @public
 */
export declare function installAlertFlashClock(): void;
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