/**
 * Returns a string formatted as spoken words.
 *
 * Converts camelCase, PascalCase, snake_case, kebab-case, or mixed alphanumeric
 * identifiers into space-separated words. Capitalizes the first word, and
 * preserves acronyms and version tokens (e.g., `v2`, `v3.1`).
 *
 * @example
 * ```ts
 * toWords("helloWorld"); // "Hello world"
 * ```
 *
 * @example
 * ```ts
 * toWords("HTML5Parser"); // "HTML 5 parser"
 * ```
 *
 * @example
 * ```ts
 * toWords("api_v2_response"); // "Api v2 response"
 * ```
 *
 * @example
 * ```ts
 * toWords("User-ID"); // "User ID"
 * ```
 *
 * @example
 * ```ts
 * toWords("employeeV3Final"); // "Employee v3 final"
 * ```
 *
 * @example
 * ```ts
 * toWords("version_2_0_release"); // "Version 2 0 release"
 * ```
 *
 * @param input A string to be returned as spoken words.
 * @returns A natural-language version of the input identifier.
 */
export declare function toWords(input: string): string;