I am using a JInternalFrame. A very nice component. I have a question
regarding what types of things can be set as its content pane.

If I set a JPanel as its content pane (as done in the swing set demo),
things work fine.

Suppose I set the content (i.e. getContentPane().add()) to be
something like JApplet.

There is a problem when you move the internal frame. It seems the
content moves disproportionately to the internal frame. The content
applet "moves out of" the internal frame.