You can not, however, use the regular function with async validations.
supports async validations through the returns a Promise that is resolved if the validation passes and is rejected if the validation failed, passing the errors as the first argument.
The errors has the same format as the errors from the regular validation function.
If the attributes objects is an HTML/DOM/j Query element Even though none of the built in validators are async it is sometimes useful to have async validations.
One example would be to check if a username is already used by asking the server.