/**
 * @param  {any} str
 * @returns {boolean}
 */
export declare function isString(str: any): boolean;
/**
 * @param  {string} filter
 * @returns {string}
 */
export declare function replaceColonByEqualSign(filter: string): string;
/**
 * @param  {any[]} arr
 * @returns {string}
 */
export declare function stringifyArray(arr: any[]): string;
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