Many letters look similar but are distinguished from one another by dots (i‘jām) above or below their central part (rasm).
As with other abjads, such as the Hebrew alphabet, scribes later devised means of indicating vowel sounds by separate vowel points. Adaptations of the Arabic script for other languages added and removed some letters, as for Kurdish, Persian, Ottoman Turkish, Sindhi, Urdu, Malay, Pashto, Arwi and Malayalam (Arabi Malayalam), all of which have additional letters as shown below.
There are no distinct upper and lower case letter forms.
Other ranges are for compatibility to older standards and contain other ligatures, which are optional.
Note: Unicode also has in its Presentation Form B FExx range a code for this ligature.
The diacritic only appears where the consonant at the end of one syllable is identical to the initial consonant of the following syllable.
(The generic term for such diacritical signs is ḥarakāt).
All Arabic vowels, long and short, follow a consonant; in Arabic, words like "Ali" or "alif", for example, start with a consonant: ‘Aliyy, alif.
In the fully vocalized Arabic text found in texts such as Quran, a long ā following a consonant other than a hamzah is written with a short a sign (fatḥah) on the consonant plus an alif after it; long ī is written as a sign for short i (kasrah) plus a yā’; and long ū as a sign for short u (ḍammah) plus a wāw. Long ā following a hamzah may be represented by an alif maddah or by a free hamzah followed by an alif.
However, in the education system and particularly in classes on Arabic grammar these vowels are used since they are crucial to the grammar.
An Arabic sentence can have a completely different meaning by a subtle change of the vowels.
The only ligature within the primary range of Arabic script in Unicode (U 06xx) is lām alif.