The default for this value is FieldValidate which is generated in the Rules.js module to provide a building block for creating validation for individual fields.
If in the generated framework additional validation functions have been written or incorporated, you can use this property to specify the validation function to use. Note that any custom validation functions should follow the same patter as the provided FieldValidate function.
This property is only shown when ValidateOnChange is true and ValidateAtHost is false.