These hints determine how the menu should be positioned in the case that the menu would fall off-screen if placed in its ideal position.

For example, [gdk.types.AnchorHints.FlipY] will replace [gdk.types.Gravity.NorthWest] with [gdk.types.Gravity.SouthWest] and vice versa if the menu extends beyond the bottom edge of the monitor.
See gtk_menu_popup_at_rect (), gtk_menu_popup_at_widget (), gtk_menu_popup_at_pointer (), #GtkMenu:rect-anchor-dx, #GtkMenu:rect-anchor-dy, #GtkMenu:menu-type-hint, and #GtkMenu::popped-up.