/** Tests if a string is hex */
export declare function isHex(str?: string): boolean;
/** Tests if a string is a 64 length hex string */
export declare function isHexKey(key?: string): boolean;
/**
 * Remove invisible characters from a string
 * @see read more https://www.regular-expressions.info/unicode.html#category
 */
export declare function stripInvisibleChar(str: string): string;
export declare function stripInvisibleChar(str?: string | undefined): string | undefined;