/**
 * Increments or decrements the number in a relative timeframe expression.
 *
 * @param currentText - The current expression (e.g. `now+1d`, `-2h`, `now`)
 * @param direction - +1 to increment, -1 to decrement
 * @returns The updated expression, or null if not spinnable
 *
 * @example
 * spinExpressionValue('now+1d', 1)   // 'now+2d'
 * spinExpressionValue('now+1d', -1)  // 'now'
 * spinExpressionValue('-2h', -1)     // '-3h'
 * spinExpressionValue('now', 1)      // 'now+1'
 * spinExpressionValue('+', 1)        // '+1'
 */
export declare function spinExpressionValue(currentText: string, direction: 1 | -1): string | null;