During that event, it will perform the validation described by the following pseudo-code: W3C Selectors Specification defines a few categories of selectors: simple, pseudo-elements, combinators.
You have to manage these errors completely manually and they should be independant with other validations. Note that Parsley triggers events that allows Parsley UI to work.
Validating functions should return either otherwise. It can instead return a j Query promise that will be resolved if the value is valid, or be rejected otherwise.
Validators can reject with a custom error message as a first argument if desired.
You can specify what kind of requirement parameter your custom validator is expecting: as second and third arguments (the first one being the value(s) to validate).
For cases where more complex parameters are needed, you can specify extra parameters; refer to the source and check how the for each locale.