جَاءَ زَيْدٌ يَبْتَسِمُ.
Zayd arrived smiling.
The affirmative imperfect 'yabtasimu' depicts an action concurrent with arrival. In the traditional rhetorical treatment, such an affirmative imperfect circumstantial clause does not directly begin with circumstantial wāw. If a seeming counterexample contains wāw, first determine whether it is coordinating another clause or whether an understood nominal construction changes the analysis.
A correct application checks three features together: affirmative imperfect form, genuinely circumstantial function, and the relevant linking structure. The mere sequence 'wāw + imperfect' is not enough to claim a genuine exception.