A toplevel window to be embedded into other processes.
This class provides the ability to embed widgets from one process into
another in a way that is transparent to the user. One process creates a
GtkSocket widget and passes the ID of that widget's
window to the other process, which then creates a
GtkPlug with that window ID. Any widgets contained in
the GtkPlug will appear inside the first
Retrieves the window ID for the plug.
Emitted when plug window is reparented to socket window.