The two behave identically, so the text is the same with s/size/window/.
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<para>
-
+#GtkWindowGroup objects are referenced by each window in the group,
+so once you have added all windows to a #GtkWindowGroup, you can drop
+the initial reference to the window group with g_object_unref(). If the
+windows in the window group are subsequently destroyed, then they will
+be removed from the window group and drop their references on the window
+group; when all window have been removed, the window group will be
+freed.
</para>
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