Add ability to override just the metadata in a struct.

service/datastore/pls.go

Index: service/datastore/pls.go
diff --git a/service/datastore/pls.go b/service/datastore/pls.go
index 86613728527adaa902537557c0f750c4fb462033..e3bb3194fb8a8d57a85f045c4c125a02c9d21306 100644
--- a/service/datastore/pls.go
+++ b/service/datastore/pls.go
@@ -86,6 +86,13 @@ import (
 //     // 'Lines' will serialized to the datastore in the field 'Lines'
 //     Lines []string
 //   }
+//
+// A pointer-to-struct may also implement MetaGetterSetter to provide more
+// sophistocated metadata values. Explicitly defined fields (as shown above)
+// always take precedence over fields manipulated by the MetaGetterSetter
+// methods. So if your GetMeta handles "kind", but you explicitly have a
+// $kind field, the $kind field will take precedence and your GetMeta
+// implementation will not be called for "kind".
 func GetPLS(obj interface{}) PropertyLoadSaver {
 	v := reflect.ValueOf(obj)
 	if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct {