A circumstantial sentence (الجملة الحالية) states a condition associated with the subject of the preceding event. Since it is a full clause, the connection to its possessor must be intelligible; otherwise it may look like a separate report.
A pronoun (ضمير) may point back to the possessor, while circumstantial wāw (واو الحالية) marks the relation in applicable forms. Neither element is invariably obligatory, and neither can always be omitted.
Example: “Jāʾa Zaydun wa-huwa yabtasim” — Zayd came while he was smiling. The pronoun huwa refers back to Zayd, and wāw makes the circumstantial relationship explicit.