/**
 * @module indicative-rules
 */
/**
 * Returns a boolean telling if value is a valid string or not.
 *
 * @example
 * ```js
 * const { is } = require('indicative')
 *
 * if (is.isString('hello world')) {
 * }
 * ```
 */
export declare const isString: (input: any) => boolean;