kustomize/site/content/en/api-reference/kustomization/namespace/_index.md

title, linkTitle, type, description

title	linkTitle	type	description
namespace	namespace	docs	Adds namespace to all resources.

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

namespace: my-namespace

Will override the existing namespace if it is set on a resource, or add it if it is not set on a resource.