Emitted to determine the position and size of any overlay child widgets.
A handler for this signal should fill
allocation with the desired position and size for
widget, relative to the
'main' child of
The default handler for this signal uses the
widget's halign and valign properties to determine the position and gives the widget
its natural size (except that an alignment of gtk_align_fill will cause the overlay to be full-width/height).
If the main child is a `GtkScrolledWindow`, the overlays are placed relative to its contents.
the child widget to position
return location for the allocation
true if the