<customwidget> <class>WidgetName</class> <extends>QWidget</extends> <header>widgetname.h</header></customwidget>
<customwidget> <class>OtherWidget</class> <extends>QWidget</extends> <header>OtherWidget.h</header></customwidget>
QString CButtonPlugin::includeFile() const{ return QLatin1String("cbutton.h");}