A GTK+ user interface is constructed by nesting widgets inside widgets. Container widgets are the inner nodes in the resulting tree of widgets: they contain other widgets. So, for example, you might have a #GtkWindow containing a #GtkFrame containing a #GtkLabel. If you wanted an image instead of a textual label inside the frame, you might replace the #GtkLabel widget with a #GtkImage widget.
Fluent builder for gtk.container.Container
Fluent builder implementation template for gtk.container.Container
Module for Container class