H3: Overview
+Overlays can be stacked, which means that more than one overlay
+can be instantiated for each database, or for the frontend.
+As a consequence, each overlay's function is called, if defined,
+when overlay execution is invoked.
+Multiple overlays are executed in reverse order (it's a stack, all in all)
+with respect to their definition in slapd.conf (5), or with respect
+to their ordering in the config database, as documented in slapd-config (5).
+
H3: Example Scenarios