* default, no recursion is done for type arguments or type bounds. But subclasses can opt to do
 * recursion by calling {@link #visit} for any {@code Type} while visitation is in progress. For
 * example, this can be used to reject wildcards or type variables contained in a type as in:
 *
 * <pre>{@code
 * new TypeVisitor() {
 *   protected void visitParameterizedType(ParameterizedType t) {

*   Added experimental support for an exactly-once visitation guarantee for evaluating Keras models trained with `tf.distribute ParameterServerStrategy`, via the `exact_evaluation_shards` argument in `Model.fit` and `Model.evaluate`.