Nooku Chain-of-Command Tutorial
Nicholas K. Dionysopoulos (@nikosdion) wrote a really nice tutorial on the Nooku Framework wiki on how to do server side validation of your data. To do this he is using a command that is placed into the command chain, and that handles validation before saving and overrides redirects when the validation fails. The command class itself is just around 30 lines of code, but can be used by any Nooku component. It is also a really good example on how to use commands in Nooku Framework.