' is optional in type suffixes for numerical literals

lib/system.nim

@@ -1662,6 +1662,10 @@ proc echo*[Ty](x: openarray[Ty]) {.magic: "Echo", noSideEffect.}
   ## available for the ECMAScript target too.
   ## Unlike other IO operations this is guaranteed to be thread-safe as
   ## ``echo`` is very often used for debugging convenience.
+  ##
+  ## As a special semantic rule, ``echo`` pretends to be free of
+  ## side effects, so that it can be used for debugging routines marked as
+  ## ``noSideEffect``.
 
 template newException*(exceptn: typeDesc, message: string): expr = 
   ## creates an exception object of type ``exceptn`` and sets its ``msg`` field