Extensibility
The validation engine in DotVVM offers several extensibility points. You can use your own validation attributes, and you can interact with the validation engine on the client-side.
Custom validation attributes
You can build your own validation attributes by implementing the IValidationAttribute class, or inheriting from the ValidationAttribute base class. See Custom attributes page in the official docs.
Client-side validation
Providing a client-side validation for custom attributes is possible by providing a custom implementation of the IValidationRuleTranslator interface, and then by registering a custom rule into dotvvm.validation.rules collection, but the process is quite complicated. We plan to make it easier in the future versions of DotVVM.
Validation events
You can subscribe to the client-side events called dotvvm.validation.events.validationErrorsChanged to be notified if the validation error collection has been changed.
You can also access the collection of all validation errors using dotvvm.validation.allErrors.