import { DocumentElement } from './types';
export declare function isValidSortIndex(sortIndex: unknown): sortIndex is string;
export declare function allElementsHaveSortIndex(elements: unknown[]): boolean;
export declare function buildKeyBetween(a: string | null, b: string | null): string;
export declare function buildNKeysBetween(a: string | null, b: string | null, n: number): string[];
export declare function compareSortIndex(a: DocumentElement, b: DocumentElement): number;