/**
 * Returns the element at a specified index in a sequence or undefined if the index is out of range.
 *
 * @export
 * @template T The type of the elements in the source sequence.
 * @param {AsyncIterable<T>} source async-iterable sequence to return the element from.
 * @param {number} index The zero-based index of the element to retrieve.
 * @param {AbortSignal} [signal] The optional abort signal to be used for cancelling the sequence at any time.
 * @returns {(Promise<T | undefined>)} An async-iterable sequence that produces the element at the specified
 * position in the source sequence, or undefined if the index is outside the bounds of the source sequence.
 */
export declare function elementAt<T>(source: AsyncIterable<T>, index: number, signal?: AbortSignal): Promise<T | undefined>;