/**
 * Convert string to upper case first letter.
 *
 * @param {string} string String to convert.
 * @returns {string}
 */
export declare function toUpperCaseFirst(string: string): string;
/**
 * Compare strings case insensitively.
 *
 * @param {...string} strings Strings to compare.
 * @returns {boolean}
 */
export declare function equalsIgnoreCase(...strings: string[]): boolean;
/**
 * Generates a random hex string. Used as namespace for Handsontable instance events.
 *
 * @returns {string} Returns 16-long character random string (eq. `'92b1bfc74ec4'`).
 */
export declare function randomString(): string;
/**
 * Checks if a string is a valid JSON object.
 *
 * @param {string} string The string to check.
 * @returns {boolean}
 */
export declare function isJSON(string: string): boolean;
/**
 * Checks if value is valid percent.
 *
 * @param {string} value The value to check.
 * @returns {boolean}
 */
export declare function isPercentValue(value: string): boolean;
/**
 * Substitute strings placed between square brackets into value defined in `variables` object. String names defined in
 * square brackets must be the same as property name of `variables` object.
 *
 * @param {string} template Template string.
 * @param {object} variables Object which contains all available values which can be injected into template.
 * @returns {string}
 */
export declare function substitute(template: string, variables?: Record<string, unknown>): string;
/**
 * Strip any HTML tag from the string.
 *
 * @param {string} string String to cut HTML from.
 * @returns {string}
 */
export declare function stripTags(string: string): string;
/**
 * Returns the string unchanged.
 *
 * @deprecated Default sanitization is now a pass-through. Use the sanitizer
 * configuration option to supply a custom sanitizer function.
 * @param {string} string String to return.
 * @returns {string}
 */
export declare function sanitize(string: string): string;
/**
 * Converts camel case to hyphens in a string.
 *
 * @param {string} str - The string to convert.
 * @returns {string} - The converted string.
 */
export declare function toHyphen(str: string): string;
/**
 * Lowercases a string in a locale-aware and performant way.
 *
 * The built-in `toLocaleLowerCase(locale)` is correct but slow — passing an explicit
 * locale forces the JavaScript engine to use its full international library on every
 * call, even for languages like German or French where the result would be exactly the
 * same as plain `toLowerCase()`. This function checks first whether the given locale
 * actually changes anything, and falls back to the faster `toLowerCase()` when it does
 * not. The check result is cached, so the overhead is paid only once per locale.
 *
 * Invalid or empty locale tags (such as `''` or `'en_US'` with an underscore instead
 * of a hyphen) are handled gracefully instead of throwing an error.
 *
 * @param {string} value The string to lowercase.
 * @param {string} [locale] A BCP 47 locale tag such as `'tr-TR'` or `'en-US'`,
 *   or `undefined` to use the host default.
 * @returns {string} The lowercased string.
 */
export declare function localeLowerCase(value: string, locale?: string): string;