If you are developing a web application then java script holds good.

of any jsf validator mechanism. Even ones that need configuring in faces-config.xml

write your own custom validator . Write your custom JSF componet wrapping
HTMLFORM JSF componet . Get your validation componet by using componet.findchildren recusrively to get your validation compont . Do your validation at decode request value phase of your component .Add JSF error if there are validation errors . those errors will be shown at render response phase of jsf life cycle.