The Validation CallOut Pattern makes it possible to add validations to generated evidence entities. The validations for a generated evidence entity are not created by the Evidence Generator. Instead, they are created by a developer in a separate file, and the Validation CallOut Pattern is used when designing the evidence entity to ensure that it can "call out" to the file that the validations are in.
When you use the Validate CallOut Pattern, the generated validate class is only generated once, so that it will not be overwritten on subsequent generations. Your developers should add this class to their own software versioning control system so that they may make modifications to it over time.