bigger comment - so we remember. #511

uSync.Core/Serialization/Serializers/DataTypeSerializer.cs

@@ -59,6 +59,24 @@ public DataTypeSerializer(IEntityService entityService, ILogger<DataTypeSerializ
         ///  datatypes are deleted late (in the last pass)
         ///  this means they are actually deleted at the very
         ///  end of the process. 
+        ///  
+        ///  In theory this should be fine, 
+        ///  
+        ///  any content types that may or may not use
+        ///  datatypes we are about to delete will have
+        ///  already been updated. 
+        /// 
+        ///  by moving the datatypes to the end we capture the 
+        ///  case where the datatype might have been replaced 
+        ///  in the content type, by not deleting first we 
+        ///  stop the triggering of any of Umbraco's delete
+        ///  processes.
+        ///  
+        ///  this only works because we are keeping the track of
+        ///  all the deletes and renames when they happen
+        ///  and we can only reliably do that for items
+        ///  that have ContainerTree's because they are not 
+        ///  real trees - but flat (each alias is unique)
         /// </remarks>
         protected override SyncAttempt<IDataType> ProcessDelete(Guid key, string alias, SerializerFlags flags)
         {