You can apply a handler to an application or a form, depending on the handler type.
For a handler, a class is required. However, in your design, you can already use the handler definition without the class defined.
Inform the developer on the requirements for the handler class to be developed.
Steps
Click Mobility design.
Click Handlers.
Click New.
In the Handler field, type a value.
In the Description field, type a value.
Close the page.
Close the page.
Notes
You can use a handler on any application.