- `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))

*   `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))

    * You can start with [Python Types Intro](https://fastapi.tiangolo.com/python-types/), it explains what changes between different Python versions, in Python 3.9 and in Python 3.10.

- 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))

* 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

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

- 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))

The precise details are relevant for Go implementations,
affect the specifics of error messages (such as whether
a compiler reports a type inference or other error),
and may explain why type inference fails in unusual code situations.
But by and large these rules can be ignored when writing Go code:
type inference is designed to mostly "work as expected",

#### 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.