Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class ethers [ROR (R≠H)]
                 dimethyl ether [C2H6O; CH3OCH3]
                 2.3.212.2 Class epoxy compounds (─O─ bridge)