To be implemented by subclasses. This method should return an instance of CPreview.
	 * Currently, the choice is between CompilationUnitPreview which contains a valid compilation
	 * unit, or a SnippetPreview which formats several independent code snippets and displays them 
	 * in the same window.
To be implemented by subclasses. This method should return an instance of CPreview.
	 * Currently, the choice is between CompilationUnitPreview which contains a valid compilation
	 * unit, or a SnippetPreview which formats several independent code snippets and displays them 
	 * in the same window. | ModifyDialogTabPage.java