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In Wicket 1.4 header contributions were rendered parent first. Since 1.5 we render the deepest child first. Now it's possible for containers, which manage their children, to supersede a childs contribution. See WICKET-2693
WicketTester.startPanel() and WicketTester.assertLabel()
WicketTester always requires a Page, no exception. For startPanel() to work, we use DummyPanelPage and add the panel. Until now assertLabel() required a path relative to page. That wasn't very intuitive, since it required you to prepend the panel-id to your label path. That has changed. Now the path relative to the Panel is sufficient.
List of renamed classes and methods
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