During Soviet rule, the city was spelled in Cyrillic as "Бакы" in Azerbaijani (while the Russian spelling was and still is "Баку", ). The modern Azerbaijani spelling, which has been using the Latin alphabet since 1991, is ; the shift from the Perso-Arabic letter و ("ū") to Cyrillic "ы" and, later, Latin "ı" may be compared to that in other Azerbaijani words (e.g. compare "qāpū" in old Perso-Arabic spelling with modern Azerbaijani , "door") or in suffixes, as و was often used to transcribe the vowel harmony in Azerbaijani (which was also the practice in Ottoman Turkish). (See also Azerbaijani alphabet.)