/**
 * Hiragana is transformed into lower case output.
 * Katakana is transformed into UPPER case output.
 * ```js
 * toRomaji('ローマじ') // === 'RŌMAji';
 * ```
 * The sequences of same vowels and 'ou' output with prolonged vowel of the first.
 * The sequence of 'ei' is not represented with long 'e'.
 * ex)
 * - 'ちちゅうかい', 'chichūkai'
 * - 'ふりょう', 'furyō'
 * - 'しょうがくせい', 'shōgakusei'
 *
 * Caveat: The rule to not consider as prolonged vowel sound
 * when the consecutive vowels are from separate Kanjis is not respected.
 *
 * ex) 'きいはんとうのばあい'
 * - OK: 'kiihantōnobaai'
 * - Our _wrong_ output: 'kīhantōnobāi'
 *
 * 'おかあさん'
 * - should be and is 'okāsan'
 *
 * 'とおり'
 * - should be and is 'tōri'
 * @param kana The input with Hiragana/Katakana
 * @returns Romaji representation of the input
 */
export declare function toRomaji(kana: string): string;