/**
 * This Source Code is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright (c) Infonomic Company Limited
 *
 * Fractional-index keys for stable, drag-and-drop reordering without a
 * rebalancing pass. Keys are base-62 strings that sort lexicographically;
 * `generateKeyBetween(a, b)` produces a new key strictly between two
 * neighbors (or before/after a single neighbor when the other is null).
 *
 * Implementation follows David Greenspan's algorithm
 * (https://observablehq.com/@dgreensp/implementing-fractional-indexing).
 * Each key has two parts: a head character that encodes the integer-part
 * length, followed by the integer digits and an optional base-62 fraction.
 * Heads 'A'..'Z' carry positive integer-part lengths 2..27; heads 'a'..'z'
 * carry negative integer-part lengths 2..27. This allows unbounded
 * prepend/append without ever needing a rebalance.
 *
 * Used by `orderable: true` collections to drive the
 * `byline_documents.order_key` column.
 */
/**
 * Validate a complete order_key — head + integer + optional fraction.
 * Returns true if the key is well-formed; false otherwise. Does not throw.
 */
export declare function validateOrderKey(key: string): boolean;
/**
 * Generate an order_key strictly between `a` and `b`.
 *
 * - `(null, null)` returns a midpoint near zero
 * - `(a, null)` returns a key greater than `a`
 * - `(null, b)` returns a key less than `b`
 * - `(a, b)` returns a key strictly between (requires `a < b`)
 *
 * Throws if `a >= b`, if either key is malformed, or if the integer
 * head is already at its extreme bound (effectively never under normal
 * use — would require ~10^40 unbounded prepends or appends).
 */
export declare function generateKeyBetween(a: string | null, b: string | null): string;
/**
 * Generate `n` order_keys strictly between `a` and `b`, in ascending order.
 * Used when inserting a contiguous run of rows (bulk import, multi-select drop).
 */
export declare function generateNKeysBetween(a: string | null, b: string | null, n: number): string[];