export declare function assertStringKey<K extends string>(thing: unknown, key: K, { errorMessage, }?: {
    errorMessage?: (key: K) => string;
}): asserts thing is Record<K, string>;
export declare function assertOneOfKeys<K extends string>(thing: unknown, keys: K[], { errorMessage, }?: {
    errorMessage?: (keys: K[]) => string;
}): asserts thing is Record<K, string>;
export declare function assertKey<K extends string>(thing: unknown, key: K, { errorMessage, }?: {
    errorMessage?: (key: K) => string;
}): asserts thing is Record<K, undefined>;
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