This article describes how you can create your custom validators by implementing javax.faces.validator.Validator interface. But one problem with this is that you need to create a separate Java class for each validation, for e.g. you would have individual Java classes for validating email, credit card number and so on. And for each Java class you have to add <validator>…</validator> entry in faces-config.xml.
Many a times while editing faces-config.xml I felt the need of content assist which could provide me with available tags and its attributes to ease development. JSF provides a DTD for faces-config.xml which can be used for this purpose.
Include this DOCTYPE in your faces-config.xml file
< !DOCTYPE faces-config PUBLIC "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.0//EN" "http://java.sun.com/dtd/web-facesconfig_1_0.dtd">