/**
 * Converts a string to Snake Case.
 *
 * @example
 * toSnakeCase("Hello World") // "hello_world"
 * toSnakeCase("CamelCaseString") // "camel_case_string"
 * toSnakeCase("") // ""
 *
 * @param str The string to convert to Snake Case.
 * @returns The Snake Case version of the input string.
 */
export declare function toSnakeCase(str: string): string;