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-rw-r--r--lib/stdlib/doc/src/gen_statem.xml10
1 files changed, 10 insertions, 0 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index 1b99b65e09..bc86415d28 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -1733,6 +1733,16 @@ handle_event(_, _, State, Data) ->
<v>Reason = term()</v>
</type>
<desc>
+ <note>
+ <p>
+ This callback is optional, so callback modules need not export it.
+ If a release upgrade/downgrade with
+ <c>Change={advanced,Extra}</c>
+ specified in the <c>.appup</c> file is made
+ when <c>code_change/4</c> is not implemented
+ the process will crash with exit reason <c>undef</c>.
+ </p>
+ </note>
<p>
This function is called by a <c>gen_statem</c> when it is to
update its internal state during a release upgrade/downgrade,