The Arabic script is cursive, and all primary letters have conditional forms for their glyphs, depending on whether they are at the beginning, middle or end of a word, so they may exhibit four distinct forms (initial, medial, final or isolated). However, six letters have only isolated or final form, and so force the following letter (if any) to take an initial or isolated form, as if there were a word break.
For compatibility with previous standards, Unicode can encode all these forms separately; however, these forms can be inferred from their joining context, using the same encoding.
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