Using the "class" Command with Spring Roo

I was taking some advice I read in a different thread to create a custom Form Backing Object for a JSP that would handle two or more entities. The advice was to create a controller, and then to use the class command to create the Form Backing Object (FBO):

Code:

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class --class ~web.fbo.NewFormWrapper

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Once you create this empty class, where do I go from here? I tried adding fields to this new class with the field command. Roo does not throw out an error, but I don't see the fields appear in this class. Should I just add them manually?