Arabic Presentation Forms-B is a Unicode block encoding spacing forms of Arabic diacritics, and contextual letter forms.
The special codepoint ZWNBSP (zero width no-break space) is also here, which is only meant for a byte order mark (that may precede text, Arabic or not, or be absent).
[note 1] The block name in Unicode 1.0 was Basic Glyphs for Arabic Language;[5] its characters were re-ordered in the process of merging with ISO 10646 in Unicode 1.0.1 and 1.1.
[3] The presentation forms are present only for compatibility with older standards, and are not currently needed for coding text.
[6] The following Unicode-related documents record the purpose and process of defining specific characters in the Arabic Presentation Forms-B block: