The basic letter form remains unchanged. In most cases, the letters transcribe consonants or consonants and a few vowels, so most Arabic alphabets are abjads. Additionally, it does not have capital letters. The script was first used to write texts in Arabic, most notably the , the holy book of Islam. With the spread of Islam, it came to be used as the primary script for many language families, leading to the addition of new letters and other symbols, with some versions, such as Kurdish, Uyghur and old Bosnian being abugidas or true alphabets. It is also the basis for the tradition of Arabic calligraphy. The Arabic script has been adapted for use in a wide variety of languages besides Arabic, including Persian, Malay and Urdu, which are not Semitic. Such adaptations may feature altered or new characters to represent phonemes that do not appear in Arabic phonology. For example, the Arabic language lacks a voiceless bilabial plosive (the sound), therefore many languages add their own letter to represent in the script, though the specific letter used varies from language to language. These modifications tend to fall into groups: Indian and Turkic languages written in the Arabic script tend to use the Persian modified letters, whereas the languages of Indonesia tend to imitate those of Jawi. The modified version of the Arabic script originally devised for use with Persian is known as the Perso-Arabic script by scholars. In the cases of Bosnian, Kurdish, Kashmiri and Uyghur writing systems, vowels are mandatory. The Arabic script can therefore be used in both abugida and abjad forms, although it is often strongly, if erroneously, connected to the latter due to it being originally used only for Arabic. Use of the Arabic script in West African languages, especially in the Sahel, developed with the spread of Islam. To a certain degree the style and usage tends to follow those of the Maghreb (for instance the position of the dots in the letters "" and ""). Additional diacritics have come into use to facilitate the writing of sounds not represented in the Arabic language. The term "", which comes from the Arabic root for "foreign," has been applied to Arabic-based orthographies of African languages. Today Iran, Afghanistan, Pakistan, India, and China are the main non-Arabic speaking states using the Arabic alphabet to write one or more official national languages, including Azerbaijani, Baluchi, Brahui, Persian, Pashto, Central Kurdish, Urdu, Sindhi, Kashmiri, Punjabi and Uyghur.