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-rw-r--r--lib/stdlib/doc/src/gen_statem.xml13
1 files changed, 13 insertions, 0 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index b20abbea5d..d19602b67c 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -1685,6 +1685,19 @@ handle_event(_, _, State, Data) ->
It is recommended to use an atom as <c>Reason</c> since
it will be wrapped in an <c>{error,Reason}</c> tuple.
</p>
+ <p>
+ Also note when upgrading a <c>gen_statem</c>,
+ this function and hence
+ the <c>Change={advanced,Extra}</c> parameter in the
+ <seealso marker="sasl:appup"><c>appup</c></seealso> file
+ is not only needed to update the internal state
+ or to act on the <c>Extra</c> argument.
+ It is also needed if an upgrade or downgrade should change
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>,
+ or else the callback mode after the code change
+ will not be honoured,
+ most probably causing a server crash.
+ </p>
</desc>
</func>