<object> are encapsulated in HTMLPlugInElement. FrameLoaderClient has a method createPlugin that returns the Widget that should be used as the plugin. FrameLoaderClientQt.cpp inspects the mimetype. With a mime type of application/x-qt-plugin or application/x-qt-styled-widget, the frameloader creates a QWidget using the QWebPluginFactory (QWebPluginFactory::create()). This QWidget is encapsulate in a QtPluginWidget (which is basically a WebCore Widget). The QWidget is created as a child of the QWebPageClient::pluginParent() (more information on this below).