According to the Unicode FAQ:
Q. Is it necessary to use the presentation forms that are defined in Unicode? A. No, it is not necessary to use those presentation forms. Those forms were
selected and identified in the early days of developing Unicode when
sophisticated rendering engines were not prevalent. A selected subset of the
presentation forms was included to provide users with a simple method to
Q. Can one use the presentation forms in a data file? A. It is strongly discouraged and not recommended because it does not
guarantee data integrity and interoperability. In the particular case of Arabic,
data files should include only the characters in the Arabic block, U+0600 to U+06FF.
Unidentified broken clients are inserting Arabic presentation forms into
articles on ar.wikipedia.org. This causes problems because some browsers do not
display these characters. I suggest we convert presentation forms to their
canonical equivalent during NFC normalisation on page save. For those rare cases
where isolated characters in specified forms are required, HTML character
entities can be used.