Explication:

These readings represent linguistic options for the same word. Many scholars maintain that the word derives from Latin strata, so in Arabic it has been pronounced in various ways. Others argue that it derives from the Arabic root s-r-ṭ (meaning 'to swallow'), so the first reading here follows the unanimous spelling in the Codices with ṣād, and the minority reading with sīn is based on the linguistic origin. *NB: in the narration of Khalaf from Ḥamzah, the ṣād is pronounced as a voiced consonant, closer to 'z' (ishmām). **Qunbul has another narration in line with the majority with a pure ṣād.