diff --git a/UPDATING b/UPDATING
--- a/UPDATING
+++ b/UPDATING
@@ -27,6 +27,17 @@
 	world, or to merely disable the most expensive debugging functionality
 	at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20250403:
+	mac_do(4) is now considered production-ready and its functionality has
+	been considerably extended at the price of breaking credentials
+	transition rules' backwards compatibility (in particular, by commit
+	6c3def74e2de; recent commit f01d26dec67f introduce backwards
+	compatibility for a specific case and for a limited transition period).
+	Please consult the mac_do(4) manual page for the new rules grammar.
+	Migrating old rules as they are is generally just a matter of adding
+	"uid=" in front of the target part, substituting commas (",") with
+	semi-colons (";") and colons (":") with greater-than signs (">").
+
 20250314:
 	We now use LLVM's binary utilities (nm, objcopy, etc.) by default.
 	The WITHOUT_LLVM_BINUTILS src.conf(5) knob can be used to revert to