What should not be generalized from kaʾayyin?

Meeting of Two Sākin Letters — ʿAlā Ḥaddih, Ghayr Ḥaddih and Tanwīn

• Considering muṣḥaf spelling
• Following the reading of Ḥafṣ
• Sounding the nūn at every normal tanwīn stop
• Recognizing a specific exception