ProtoSMILES supports "aromatic bonds" (":"), but Balsa does not. Despite clear inclusion within the syntax of ProtoSMILES, no precise guidance on using aromatic bonds is provided. Weininger notes that "Adjacent atoms without an intervening bond symbol are connected by a valence-dictated bond (typically a single or aromatic bond) '-' (single) and ':' (aromatic) bond symbols may always be omitted on input" ]. This passage implies that aromatic bonds serve no purpose. Accordingly, Balsa does not allow them and the syntax does not include the colon symbol (:).