WIP add footnote about Chaing Growth "requirement"

docs/website/contents/for-developers/CivicTime.md

@@ -160,9 +160,12 @@ The exact thought process was not recorded during the design work, but this is a
     It would also be too confusing if a node agreed to translate some slot/civic time and then subsequently refused to translate that same slot/civic time.
     So `Just t1 -> Nothing` is also unacceptable for some translation, not merely `Just t1 -> Just t2`.
 
-  - {DespiteChainGrowthViolation}.
+  - {DespiteChainGrowthViolation}[^Anachrony].
     All of the above must hold even in the presence of a Chain Growth violation, except switching from a chain that violates Chain Growth to one that does not is allowed to violate the RollbackInsensitiveTranslations subcase of ImmutableTranslations.
 
+[^Anachrony]: Clarification.
+    This was not originally a "requirement", but the behavior was eventually discovered and has so far been accepted as reasonable and potentially even desirable.
+
 **{Iteration 1}**.
 The ImmutableTranslations and NonemptyForecastRange requirements are simple to achieve without the rest.