code: static <T> Node.Builder<T> builder(long exactSizeIfKnown, IntFunction<T[]> generator) {
          return (exactSizeIfKnown >= 0 && exactSizeIfKnown < MAX_ARRAY_SIZE)
                 ? new FixedNodeBuilder<>(exactSizeIfKnown, generator)
                 : builder();
      }
docs: Produces a {@link Node.Builder}.
  
  @param exactSizeIfKnown -1 if a variable size builder is requested,
  otherwise the exact capacity desired.  A fixed capacity builder will
  fail if the wrong number of elements are added to the builder.
  @param generator the array factory
  @param <T> the type of elements of the node builder
  @return a {@code Node.Builder}