Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class cations [X+]
                 Class onium compounds
                   Class halonium ions [R2X+ (X=halogen)]
                     Class chloronium ions [R2Cl+]
                       1 chloronium [H2Cl+]