import type { MessageExpressionPart } from '../formatted-parts.ts';
import type { MessageValue } from '../message-value.ts';
/**
 * Used to represent runtime/formatting errors.
 */
export interface MessageFallback extends MessageValue<'fallback'> {
    readonly type: 'fallback';
    readonly source: string;
    toParts(): [MessageFallbackPart];
    toString(): string;
}
/** @category Formatted Parts */
export interface MessageFallbackPart extends MessageExpressionPart<'fallback'> {
    type: 'fallback';
    source: string;
}
export declare const fallback: (source?: string) => MessageFallback;