Provides methods to register user exit classes for accounts, contacts, and leads. User exit classes must be registered to invoke the implementer class. The class name specified as a parameter value must contain the namespace prefix <<NameSpacePrefix.ClassName>> if the implementing class is in some other managed package. If the implementing class is part of an inner class that is not part of a managed package, then the format is <<OuterClassName.InnerClassName>>. If the implementing class is part of an outer class, then the format is <<ClassName>>.