code: public void init(IEditorSite site, IEditorInput editorInput) throws PartInitException {
  		if (!(editorInput instanceof IFileEditorInput))
  			throw new PartInitException("Invalid Input: Must be IFileEditorInput");
  		super.init(site, editorInput);
  	}
docs: The <code>MultiPageEditorExample</code> implementation of this method
  checks that the input is an instance of <code>IFileEditorInput</code>.