Block from U+FE70 to U+FEFF. This block was introduced in Unicode version 1.1 (1993). It contains 141 codepoints.
The Wikipedia provides the following information on block Arabic Presentation Forms-B:
Arabic Presentation Forms-B is a Unicode block encoding spacing forms of Arabic diacritics, and contextual letter forms. The presentation forms are present only for compatibility with older standards, and are not currently needed for coding text.