code: public static <K,V> Level0MapOperator<Map<K,V>,K,V> onMapOf(final Type<K> keyType, final Type<V> valueType, final Map<? extends K,? extends V> target) {
          return new Level0MapOperator<Map<K,V>,K,V>(ExecutionTarget.forOp(target, Normalisation.MAP));
      }
docs: <p>
  Creates an <i>operation expression</i> on the specified target object, specifying the
  target map key and value types by means of the <tt>keyType</tt> and <tt>valueType</tt>
  parameters.
  </p>
  
  @param keyType the type of the map keys
  @param valueType the type of the map values
  @param target the target object on which the expression will execute
  @return an operator, ready for chaining