-The argument was added in Exim version 4.90 - changing the API.
-Nobody noticed until 4.93 was imminent.
-A decision on the way forward has not yet been made.
+The argument was added in Exim version 4.90 - changing the API/ABI.
+Nobody noticed until 4.93 was imminent, at which point the
+ABI version number was incremented.