The conclusion of a discussion with robertoemanuel was that the following changes should be made to the ValidationService API. Most notably was the desire to have an explicit "clear" method (rather than setting with a valid state) this was because Reducers should explicitly clear existing validation for a model sub-tree before re-validating. Problems had been noticed with the call to set a valid state when validating collections of items that may have entries deleted.

• Remove use of ValidationLevel.VALID
• Add ValidationRegistry.clear(path)
• Add ValidationService.clear(path)
• Change ValidationService.setValidation(..) to just accept Warning/Errors.
• Change reducers to clear validation before setting (UPDATES and DELETES, and MOVES for DD)