code: @SafeVarargs
      public static <Item> void flatten(final Collection<? super Item> target, final Item... items) {
          flattenAsStream(items).forEachOrdered(target::add);
      }
docs: Recursively appends all Items specified as a comma separated list to the specified {@link Collection}.
  
  @param <Item>
  type of the array items
  
  @param items
  comma separated sequence of Items
  
  @param target
  target {@link Collection} of Items