diff --git a/staging/src/k8s.io/apimachinery/pkg/api/validation/objectmeta.go b/staging/src/k8s.io/apimachinery/pkg/api/validation/objectmeta.go
index 8b77c641c4b..7c1c690544e 100644
--- a/staging/src/k8s.io/apimachinery/pkg/api/validation/objectmeta.go
+++ b/staging/src/k8s.io/apimachinery/pkg/api/validation/objectmeta.go
@@ -44,6 +44,7 @@ var BannedOwners = map[schema.GroupVersionKind]struct{}{
 func ValidateAnnotations(annotations map[string]string, fldPath *field.Path) field.ErrorList {
 	allErrs := field.ErrorList{}
 	for k := range annotations {
+		// The rule is QualifiedName except that case doesn't matter, so convert to lowercase before checking.
 		for _, msg := range validation.IsQualifiedName(strings.ToLower(k)) {
 			allErrs = append(allErrs, field.Invalid(fldPath, k, msg))
 		}