When rich:validator find validation error then it raises JS event that is handled by rich:message and the validation error message is show.
However we can't i.e. toggle error class on input label, the input itself and do other crazy stuff.
It would be great if rich:validator had onmessage and onclear attributes so that user could bind JS callbacks that would do custom magic.
Currently rich:validator contains "onerror" attribute but it conecerns ajax request error (it's the same as in a4j:ajax), so we can't use it.