*   `kubectl explain` now explains `apiservices` and `customresourcedefinition`. (Updated to use OpenAPI instead of Swagger 1.2.) ([#53228](https://github.com/kubernetes/kubernetes/pull/53228),[ @apelisse](https://github.com/apelisse))

* Kubectl explain now prints out the Kind and API version of the resource being explained. ([#55689](https://github.com/kubernetes/kubernetes/pull/55689), [@luksa](https://github.com/luksa))

### Cluster Lifecycle

- Added `--output plaintext-openapiv2` argument to kubectl explain to use old openapiv2 `explain` implementation. ([#115480](https://github.com/kubernetes/kubernetes/pull/115480), [@alexzielenski](https://github.com/alexzielenski))

- Fixed bug where explain was not properly respecting jsonpaths. ([#115694](https://github.com/kubernetes/kubernetes/pull/115694), [@mpuckett159](https://github.com/mpuckett159))

- Eviction requests for pods that have a non-zero DeletionTimestamp will always succeed ([#91342](https://github.com/kubernetes/kubernetes/pull/91342), [@michaelgugino](https://github.com/michaelgugino)) [SIG Apps]
- Explain CRDs whose resource name are the same as builtin objects ([#89505](https://github.com/kubernetes/kubernetes/pull/89505), [@knight42](https://github.com/knight42)) [SIG API Machinery, CLI and Testing]

- `kubeadm`: updated warning message when swap space is detected. When swap is
  active on Linux, `kubeadm` explains that swap is supported for cgroup v2 only and
  is beta but disabled by default. ([#120198](https://github.com/kubernetes/kubernetes/pull/120198), [@pacoxu](https://github.com/pacoxu))

- Fixed `kubectl explain` to show enum for field types if they were defined. ([#123023](https://github.com/kubernetes/kubernetes/pull/123023), [@ah8ad3](https://github.com/ah8ad3))

#### CustomResourceDefinition OpenAPI Publishing

OpenAPI specs for native types have long been served at /openapi/v2, and they are consumed by a number of components, notably kubectl client-side validation, kubectl explain and OpenAPI based client generators.

With Kubernetes 1.15 as beta, OpenAPI schemas are also published for CRDs, as long as their schemas are structural.

- Adds alpha --output plaintext protected by environment variable `KUBECTL_EXPLAIN_OPENAPIV3` ([#113146](https://github.com/kubernetes/kubernetes/pull/113146), [@alexzielenski](https://github.com/alexzielenski)) [SIG CLI]