Hierarchical modification means that elements one or more levels down in the instantiation hierarchy are modified. Such modifiers can use nested notation, using parenthesis, or dot notation.
Two instances of the filter with different time constants T are put together to form the class FiltersInSeries.
Finally, two different instances F12 and F34 of FiltersInSeries are created in the class ModifiedFiltersInSeries with modified time constants. Both instances have identical time constants, but the first uses nested notation and the second uses dot notation for hierarchical modification.
Another example of hierarchical modification is shown for the class A, where the instance nested uses nested syntax and the instance dot uses dot notation.