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- The appearance of any menus.
- Available menu options.
- The appearance of a message box.
- The Cascading Style Sheet to be applied.
- Access to common JavaScript functions.
- Definition of any global hidden fields.
- Standard variable definitions which may be referenced in other weblets.
- Whether a visual layout should be applied.
Of course if you define your own layout, you can decide what common elements need to be included in the interface.