import ( metav1 "k8s.io/apimachinery/pkg/apis/meta/v1" "k8s.io/apimachinery/pkg/runtime" "k8s.io/apimachinery/pkg/util/intstr" "k8s.io/kubernetes/pkg/runtime/schema" ) func main() { scheme := runtime.NewScheme() scheme.AddDefaultingFuncs(DefaultServiceAccountTokenVolumeProjection) scheme.AddKnownTypes(schema.GroupVersion{Group: "", Version: "v1"}, &metav1.ObjectMeta{}) scheme.AddKnownTypes(schema.GroupVersion{Group: "apps", Version: "v1"}, &metav1.ObjectMeta{}) // ... } func DefaultServiceAccountTokenVolumeProjection(obj runtime.Object) { podSpec, ok := obj.(*PodSpec) if !ok { return } for i, volume := range podSpec.Volumes { proj, ok := volume.VolumeSource.Projection.(*ServiceAccountTokenProjection) if !ok || len(proj.Audience) > 0 { continue } podSpec.Volumes[i].VolumeSource.Projection.(*ServiceAccountTokenProjection).Audience = "api" } }In this example, `DefaultServiceAccountTokenVolumeProjection` is a function that implements the defaulting behavior for a Kubernetes object schema. This function is registered with the runtime scheme using `Scheme.AddDefaultingFuncs`. When creating or modifying objects using this scheme, the defaulting function will be run automatically. Overall, `go k8s.io/kubernetes.pkg.runtime` provides a variety of useful functions and data types for working with Kubernetes API objects in Go applications. With the `Scheme.AddDefaultingFuncs` function and others like it, developers can customize and extend the behavior of Kubernetes API objects to suit their needs.