title: REST - When to use 400 ("Bad Request")
body: <p>I have a resource like this sales/customers/{customerno}. If a client sends a PUT request to this resource I would return 400 - Bad request if the xml in the entity body is not valid xml. But what if the xml is valid, but the content of the xml is not valid. Say for instance that the client is trying to update the customers PostCode and is providing a PostCode which is not valid. Is it correct to return 400 - Bad request in this case, or is it another http code I should have used?</p>