code: public static <K,V> Level0MapOperator<Map<K,V>,K,V> onMapOf(final Type<K> keyType, Type<V> valueType) {
          return new Level0MapOperator<Map<K,V>,K,V>(ExecutionTarget.forFn(Normalisation.MAP));
      }
docs: <p>
  Creates a <i>function expression</i> for building a function operating on
  a target object of type Map&lt;K,V&gt;, being both
  <tt>Type&lt;K&gt;</tt> and <tt>Type&lt;V&gt;</tt> type specified
  as parameters.
  </p>
  <p>
  This is equivalent to <tt>Fn.on(Types.mapOf(keyType, valueType))</tt>
  </p>
  
  @param keyType the type to be used for keys
  @param valueType the type to be used for values
  @return an operator, ready for chaining