More clarifications

Author: apelisse

keps/sig-api-machinery/1929-built-in-default/README.md

@@ -201,11 +201,13 @@ Currently, null values trigger an error when nullable is false and don't
 get defaulted if a default is available. We propose to start defaulting
 fields with null values if a default is available, or the field will be
 removed if no default exists, but only when the openapi nullable flag is
-missing or false. We assume that existing APIs that use nullable are
-happy with null values. Also, people can remove the nullable attribute
-if they want null values to start being removed. This will help
-aligning CRDs and built-in types (there are no ways to set nullable to
-true for built-in types).
+missing or false. This means that will start accepting inputs that were
+rejected in the past (there is code that would work with a new server
+but not with an old server). We assume that existing APIs that use
+nullable are happy with null values. Also, people can remove the
+nullable attribute if they want null values to start being removed. This
+will help aligning CRDs and built-in types (there are no ways to set
+nullable to true for built-in types).
 
 Note that we still consider `{}` (and 0, 0.0, "", false, []) to be
 different from `null`, so `{"foo": {}}` is different from `{}` or from
@@ -431,6 +433,10 @@ type Object struct {
 }
 ```
 
+Non-pointer fields that have a default must be omitEmpty. Kubebuilder
+and built-in defaulting generators should both prevent these from
+happening.
+
 This would generate the following OpenAPI:
 ```yaml
 Object: