DeviceDecisive question
TadhyīlDoes a new independent clause reinforce or generalize the preceding point?
IḥtirāsDoes the addition prevent an unintended inference?
TatmīmDoes it add a useful feature without correcting an earlier possible misunderstanding?
In «وَجَاءَ زَيْدٌ مُبْتَسِمًا», “smiling” is a circumstantial modifier. Its grammatical optionality does not by itself prove the rhetorical device of tatmīm. The relevant expressive gain must first be established.