ValidationStrategy

FailFast strategy goes through all Rules of a Form in order, and stops validation as soon as a single error is encountered, and populates the resulting Input.Invalid with that single error. So the list of errors will always contain just one element.

LazyEval iterates through all Rules of a Form in order until all rules are exhausted, and then returns the list of errors in the resulting Input.Invalid. When using this strategy, the list of inputs may contain more than one error.