//  * URI is much more strict than HttpUrl or URL on what's accepted.
    //
    // HttpUrl is quite lenient with what characters it accepts. In particular, characters like '{'
    // and '"' are permitted but unlikely to occur in real-world URLs. Unfortunately we can't just
    // lock it down due to URL templating: "http://{env}.{dc}.example.com".
    UrlComponentEncodingTester
      .newInstance()

### Feature

### Other notable changes

* CustomResourceDefinitions: OpenAPI v3 validation schemas containing `$ref`references are no longer permitted (valid references could not be constructed previously because property ids were not permitted either). Before upgrading, ensure CRD definitions do not include those `$ref` fields. ([#58438](https://github.com/kubernetes/kubernetes/pull/58438), [@carlory](https://github.com/carlory))

  - PriorityClass resources will no longer be served from `scheduling.k8s.io/v1beta1` and `scheduling.k8s.io/v1alpha1` in v1.17. Migrate to the `scheduling.k8s.io/v1` API, available since v1.14. Existing persisted data can be retrieved via the `scheduling.k8s.io/v1` API.

    The Panther took pie-crust, and gravy, and meat,
    While the Owl had the dish as its share of the treat.
    When the pie was all finished, the Owl, as a boon,
    Was kindly permitted to pocket the spoon:
    While the Panther received knife and fork with a growl,
    And concluded the banquet--]

  `What IS the use of repeating all that stuff,' the Mock Turtle

  - NetworkPolicy resources will no longer be served from `extensions/v1beta1` in v1.16. Migrate use to the `networking.k8s.io/v1` API, available since v1.8. Existing persisted data can be retrieved via the `networking.k8s.io/v1` API.

* CustomResourceDefinitions: OpenAPI v3 validation schemas containing `$ref`references are no longer permitted (valid references could not be constructed previously because property ids were not permitted either). Before upgrading, ensure CRD definitions do not include those `$ref` fields. ([#58438](https://github.com/kubernetes/kubernetes/pull/58438), [@carlory](https://github.com/carlory))

- Kube-apiserver: The NodeRestriction admission plugin now restricts Node labels kubelets are permitted to set when creating a new Node to the `--node-labels` parameters accepted by kubelets in 1.16+. ([#90307](https://github.com/kubernetes/kubernetes/pull/90307), [@liggitt](https://github.com/liggitt)) [SIG Auth and Node]

        try {
            Files.deleteIfExists(handleFile);
            log.debug("Removed persisted handle file: {}", handleFile);
        } catch (IOException e) {
            log.error("Failed to remove persisted handle file: " + handleFile, e);
        }
    }

    private void loadPersistedHandles() {
        if (!Files.exists(stateDirectory)) {

- Kube-apiserver: events created via the `events.k8s.io` API group for cluster-scoped objects are now permitted in the default namespace as well for compatibility with events clients and the `v1` API ([#100125](https://github.com/kubernetes/kubernetes/pull/100125), [@h4ghhh](https://github.com/h4ghhh))