Why does $SO_3$ act as an electrophile?

(N/A) The $SO_3$ molecule consists of a central sulphur atom bonded to three oxygen atoms.
Due to the high electronegativity of oxygen,the electron density is pulled towards the oxygen atoms,creating a significant partial positive charge on the sulphur atom.
Furthermore,resonance structures of $SO_3$ show that the sulphur atom carries a formal positive charge in its contributing structures.
Because of this electron-deficient nature at the sulphur centre,$SO_3$ acts as an electrophile,meaning it is an electron-seeking species.