/**
 * Deep merges one object into another object, optionally at a specific path.
 *
 * @param target - The target object to merge into
 * @param source - The source object to merge from
 * @param path - Optional dot-separated path where the merge should occur (e.g., 'user.profiles.0.transactions')
 * @returns The merged object (modifies the target object)
 *
 * @example
 * ```ts
 * // Basic deep merge
 * const target = { a: 1, b: { c: 2 } };
 * const source = { b: { d: 3 }, e: 4 };
 * const result = deepMerge(target, source);
 * // { a: 1, b: { c: 2, d: 3 }, e: 4 }
 * ```
 *
 * @example
 * ```ts
 * // Merge at specific path
 * const target = {
 *   user: {
 *     profiles: [
 *       { id: 1, transactions: { count: 5 } }
 *     ]
 *   }
 * };
 * const source = { total: 100, recent: ['tx1', 'tx2'] };
 * deepMerge(target, source, 'user.profiles.0.transactions');
 * // Result: target.user.profiles[0].transactions now has count, total, and recent properties
 * ```
 *
 * @example
 * ```ts
 * // Array handling - arrays are replaced, not merged
 * const target = { items: [1, 2, 3] };
 * const source = { items: [4, 5] };
 * deepMerge(target, source);
 * // { items: [4, 5] } - arrays are replaced
 * ```
 */
export declare function deepMerge<T extends Record<string, any>>(target: T, source: Record<string, any>, path?: string): T;