Bins are widgets with exactly one child widget. They are constructed
bin function, given a GTK+ widget constructor, a list of
attributes, and a child widget.
bin Window [#title := "Example Window"] $ widget Label [#label := "Nothing here yet."]
In some cases, specific types of bins are used as children of other
widgets. In the case of
ListBox, we use
ListBoxRow bins as
container ListBox  [ bin ListBoxRow  $ widget Button  , bin ListBoxRow  $ widget CheckButton  ]
To find which GTK+ widgets are bins, use the Haddock
documentation of gi-gtk and look for objects with instances of the
IsBin type class.