Merge branch 'raimo/gen_statem-improvements/OTP-13929' into maint

* raimo/gen_statem-improvements/OTP-13929:
  Fix race condition in cancel_timer/1
  Use parameterized types
  Implement state timeouts
  Improve docs and types
  Change state entry events into state enter calls
  Improve docs
  Improve docs
  Implement state entry events
  Implement call/3 dirty_timeout

9 files changed, 1779 insertions, 804 deletions

diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index 3322571b2c..64267c2af5 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -54,7 +54,8 @@
       <p>
         This is a new behavior in Erlang/OTP 19.0.
         It has been thoroughly reviewed, is stable enough
-        to be used by at least two heavy OTP applications, and is here to stay.
+        to be used by at least two heavy OTP applications,
+	and is here to stay.
         Depending on user feedback, we do not expect
         but can find it necessary to make minor
         not backward compatible changes into Erlang/OTP 20.0.
@@ -70,6 +71,7 @@
       <item>The state can be any term.</item>
       <item>Events can be postponed.</item>
       <item>Events can be self-generated.</item>
+      <item>Automatic state enter code can be called.</item>
       <item>A reply can be sent from a later state.</item>
       <item>There can be multiple <c>sys</c> traceable replies.</item>
     </list>
@@ -125,9 +127,9 @@ erlang:'!'            -----> Module:StateName/3
       is not regarded as an error but as a valid return
       from all callback functions.
     </p>
-    <marker id="state_function"/>
+    <marker id="state callback"/>
     <p>
-      The "<em>state function</em>" for a specific
+      The "<em>state callback</em>" for a specific
       <seealso marker="#type-state">state</seealso>
       in a <c>gen_statem</c> is the callback function that is called
       for all events in this state. It is selected depending on which
@@ -139,7 +141,7 @@ erlang:'!'            -----> Module:StateName/3
       When the
       <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
       is <c>state_functions</c>, the state must be an atom and
-      is used as the state function name; see
+      is used as the state callback name; see
       <seealso marker="#Module:StateName/3"><c>Module:StateName/3</c></seealso>.
       This gathers all code for a specific state
       in one function as the <c>gen_statem</c> engine
@@ -152,7 +154,7 @@ erlang:'!'            -----> Module:StateName/3
       When the
       <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
       is <c>handle_event_function</c>, the state can be any term
-      and the state function name is
+      and the state callback name is
       <seealso marker="#Module:handle_event/4"><c>Module:handle_event/4</c></seealso>.
       This makes it easy to branch depending on state or event as you desire.
       Be careful about which events you handle in which
@@ -162,8 +164,8 @@ erlang:'!'            -----> Module:StateName/3
     <p>
       The <c>gen_statem</c> enqueues incoming events in order of arrival
       and presents these to the
-      <seealso marker="#state_function">state function</seealso>
-      in that order. The state function can postpone an event
+      <seealso marker="#state callback">state callback</seealso>
+      in that order. The state callback can postpone an event
       so it is not retried in the current state.
       After a state change the queue restarts with the postponed events.
     </p>
@@ -175,12 +177,12 @@ erlang:'!'            -----> Module:StateName/3
       to entering a new receive statement.
     </p>
     <p>
-      The <seealso marker="#state_function">state function</seealso>
+      The <seealso marker="#state callback">state callback</seealso>
       can insert events using the
       <seealso marker="#type-action"><c>action()</c></seealso>
       <c>next_event</c>
       and such an event is inserted as the next to present
-      to the state function. That is, as if it is
+      to the state callback. That is, as if it is
       the oldest incoming event. A dedicated
       <seealso marker="#type-event_type"><c>event_type()</c></seealso>
       <c>internal</c> can be used for such events making them impossible
@@ -193,9 +195,19 @@ erlang:'!'            -----> Module:StateName/3
       <seealso marker="gen_fsm"><c>gen_fsm</c></seealso>
       to force processing an inserted event before others.
     </p>
+    <p>
+      The <c>gen_statem</c> engine can automatically
+      make a specialized call to the
+      <seealso marker="#state callback">state callback</seealso>
+      whenever a new state is entered; see 
+      <seealso marker="#type-state_enter"><c>state_enter()</c></seealso>.
+      This is for writing code common to all state entries.
+      Another way to do it is to insert events at state transitions,
+      but you have to do so everywhere it is needed.
+    </p>
     <note>
       <p>If you in <c>gen_statem</c>, for example, postpone
-        an event in one state and then call another state function
+        an event in one state and then call another state callback
         of yours, you have not changed states and hence the postponed event
         is not retried, which is logical but can be confusing.
       </p>
@@ -224,7 +236,7 @@ erlang:'!'            -----> Module:StateName/3
       The <c>gen_statem</c> process can go into hibernation; see
       <seealso marker="proc_lib#hibernate/3"><c>proc_lib:hibernate/3</c></seealso>.
       It is done when a
-      <seealso marker="#state_function">state function</seealso> or
+      <seealso marker="#state callback">state callback</seealso> or
       <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
       specifies <c>hibernate</c> in the returned
       <seealso marker="#type-action"><c>Actions</c></seealso>
@@ -282,7 +294,7 @@ init([]) ->
     {ok,State,Data}.
 callback_mode() -> state_functions.
 
-%%% State function(s)
+%%% state callback(s)
 
 off({call,From}, push, Data) ->
     %% Go to 'on', increment count and reply
@@ -336,7 +348,7 @@ ok
     <code type="erl">
 callback_mode() -> handle_event_function.
 
-%%% State function(s)
+%%% state callback(s)
 
 handle_event({call,From}, push, off, Data) ->
     %% Go to 'on', increment count and reply
@@ -470,6 +482,10 @@ handle_event(_, _, State, Data) ->
       <name name="state"/>
       <desc>
 	<p>
+	  If the
+	  <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
+	  is <c>handle_event_function</c>,
+	  the state can be any term.
 	  After a state change (<c>NextState =/= State</c>),
 	  all postponed events are retried.
 	</p>
@@ -483,6 +499,8 @@ handle_event(_, _, State, Data) ->
 	  <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
 	  is <c>state_functions</c>,
 	  the state must be of this type.
+	  After a state change (<c>NextState =/= State</c>),
+	  all postponed events are retried.
 	</p>
       </desc>
     </datatype>
@@ -515,7 +533,22 @@ handle_event(_, _, State, Data) ->
 	  Type <c>info</c> originates from regular process messages sent
 	  to the <c>gen_statem</c>. Also, the state machine
 	  implementation can generate events of types
-	  <c>timeout</c> and <c>internal</c> to itself.
+	  <c>timeout</c>, <c>state_timeout</c>, <c>enter</c>,
+	  and <c>internal</c> to itself.
+	</p>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="callback_mode_result"/>
+      <desc>
+	<p>
+	  This is the return type from
+	  <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>
+	  and selects 
+	  <seealso marker="#type-callback_mode">callback mode</seealso>
+	  and whether to do
+	  <seealso marker="#type-state_enter">state enter calls</seealso>,
+	  or not.
 	</p>
       </desc>
     </datatype>
@@ -551,13 +584,58 @@ handle_event(_, _, State, Data) ->
       </desc>
     </datatype>
     <datatype>
+      <name name="state_enter"/>
+      <desc>
+	<p>
+	  If the state machine should use <em>state enter calls</em>
+	  is selected when starting the  <c>gen_statem</c>
+	  and after code change using the return value from
+	  <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>.
+	</p>
+	<p>
+	  If 
+	  <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>
+	  returns a list containing <c>state_enter</c>,
+	  the <c>gen_statem</c> engine will, at every state change,
+	  call the
+	  <seealso marker="#state callback">state callback</seealso>
+	  with arguments <c>(enter, OldState, Data)</c>.
+	  This may look like an event but is really a call
+	  performed after the previous state callback returned
+	  and before any event is delivered to the new state callback.
+	  See
+	  <seealso marker="#Module:StateName/3"><c>Module:StateName/3</c></seealso>
+	  and
+	      <seealso marker="#Module:handle_event/4"><c>Module:handle_event/4</c></seealso>.
+	</p>
+	<p>
+	  If 
+	  <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>
+	  does not return such a list, no state enter calls are done.
+	</p>
+	<p>
+	  If 
+	  <seealso marker="#Module:code_change/4"><c>Module:code_change/4</c></seealso>
+	  should transform the state to a state with a different
+	  name it is still regarded as the same state so this
+	  does not cause a state enter call.
+	</p>
+	<p>
+	  Note that a state enter call <em>will</em> be done
+	  right before entering the initial state even though this
+	  formally is not a state change.
+	  In this case <c>OldState</c> will be the same as <c>State</c>,
+	  which can not happen for a subsequent state change.
+	</p>
+      </desc>
+    </datatype>
+    <datatype>
       <name name="transition_option"/>
       <desc>
 	<p>
 	  Transition options can be set by
 	  <seealso marker="#type-action">actions</seealso>
-	  and they modify the following in how
-	  the state transition is done:
+	  and they modify how the state transition is done:
 	</p>
 	<list type="ordered">
 	  <item>
@@ -586,27 +664,46 @@ handle_event(_, _, State, Data) ->
 	      All events stored with
 	      <seealso marker="#type-action"><c>action()</c></seealso>
 	      <c>next_event</c>
-	      are inserted in the queue to be processed before
-	      all other events.
+	      are inserted to be processed before the other queued events.
+            </p>
+	  </item>
+	  <item>
+            <p>
+	      If the state changes or is the initial state, and
+	      <seealso marker="#type-state_enter"><em>state enter calls</em></seealso>
+	      are used, the <c>gen_statem</c> calls
+	      the new state callback with arguments
+	      <seealso marker="#type-state_enter">(enter, OldState, Data)</seealso>.
+	      Any 
+	      <seealso marker="#type-enter_action"><c>actions</c></seealso>
+	      returned from this call are handled as if they were
+	      appended to the actions 
+	      returned by the state callback that changed states.
             </p>
 	  </item>
 	  <item>
 	    <p>
-	      If an
+	      If there are enqueued events the (possibly new)
+	      <seealso marker="#state callback">state callback</seealso>
+	      is called with the oldest enqueued event,
+	      and we start again from the top of this list.
+	    </p>
+	  </item>
+	  <item>
+	    <p>
+	      Timeout timers 
+              <seealso marker="#type-state_timeout"><c>state_timeout()</c></seealso>
+	      and 
               <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso>
-	      is set through
-	      <seealso marker="#type-action"><c>action()</c></seealso>
-	      <c>timeout</c>,
-	      an event timer can be started or a time-out zero event
-	      can be enqueued.
+	      are handled.  This may lead to a time-out zero event
+	      being generated to the
+	      <seealso marker="#state callback">state callback</seealso>
+	      and we start again from the top of this list.
 	    </p>
 	  </item>
 	  <item>
 	    <p>
-	      The (possibly new)
-	      <seealso marker="#state_function">state function</seealso>
-	      is called with the oldest enqueued event if there is any,
-	      otherwise the <c>gen_statem</c> goes into <c>receive</c>
+	      Otherwise the <c>gen_statem</c> goes into <c>receive</c>
 	      or hibernation
 	      (if
 	      <seealso marker="#type-hibernate"><c>hibernate()</c></seealso>
@@ -614,8 +711,11 @@ handle_event(_, _, State, Data) ->
 	      to wait for the next message. In hibernation the next
 	      non-system event awakens the <c>gen_statem</c>, or rather
 	      the next incoming message awakens the <c>gen_statem</c>,
-	      but if it is a system event
-	      it goes right back into hibernation.
+	      but if it is a system event it goes right back into hibernation.
+	      When a new message arrives the 
+	      <seealso marker="#state callback">state callback</seealso>
+	      is called with the corresponding event,
+	      and we start again from the top of this list.
 	    </p>
 	  </item>
 	</list>
@@ -657,34 +757,65 @@ handle_event(_, _, State, Data) ->
 	  <seealso marker="#type-event_type"><c>event_type()</c></seealso>
 	  <c>timeout</c>
 	  after this time (in milliseconds) unless another
-	  event arrives in which case this time-out is cancelled.
-	  Notice that a retried or inserted event
-	  counts like a new in this respect.
+	  event arrives or has arrived
+	  in which case this time-out is cancelled.
+	  Note that a retried, inserted or state time-out zero
+	  events counts as arrived.
 	</p>
 	<p>
 	  If the value is <c>infinity</c>, no timer is started, as
-	  it never triggers anyway.
+	  it never would trigger anyway.
 	</p>
 	<p>
-	  If the value is <c>0</c>, the time-out event is immediately enqueued
-	  unless there already are enqueued events, as the
-	  time-out is then immediately cancelled.
-	  This is a feature ensuring that a time-out <c>0</c> event
-	  is processed before any not yet received external event.
+	  If the value is <c>0</c> no timer is actually started,
+	  instead the the time-out event is enqueued to ensure
+	  that it gets processed before any not yet
+	  received external event.
 	</p>
 	<p>
-	  Notice that it is not possible or needed to cancel this time-out,
+	  Note that it is not possible or needed to cancel this time-out,
 	  as it is cancelled automatically by any other event.
 	</p>
       </desc>
     </datatype>
     <datatype>
+      <name name="state_timeout"/>
+      <desc>
+	<p>
+	  Generates an event of
+	  <seealso marker="#type-event_type"><c>event_type()</c></seealso>
+	  <c>state_timeout</c>
+	  after this time (in milliseconds) unless the <c>gen_statem</c>
+	  changes states (<c>NewState =/= OldState</c>)
+	  which case this time-out is cancelled.
+	</p>
+	<p>
+	  If the value is <c>infinity</c>, no timer is started, as
+	  it never would trigger anyway.
+	</p>
+	<p>
+	  If the value is <c>0</c> no timer is actually started,
+	  instead the the time-out event is enqueued to ensure
+	  that it gets processed before any not yet
+	  received external event.
+	</p>
+	<p>
+	  Setting this timer while it is running will restart it with
+	  the new time-out value.  Therefore it is possible to cancel
+	  this timeout by setting it to <c>infinity</c>.
+	</p>
+      </desc>
+    </datatype>
+    <datatype>
       <name name="action"/>
       <desc>
 	<p>
 	  These state transition actions can be invoked by
 	  returning them from the
-	  <seealso marker="#state_function">state function</seealso>, from
+	  <seealso marker="#state callback">state callback</seealso>
+	  when it is called with an
+	  <seealso marker="#type-event_type">event</seealso>,
+	  from
 	  <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
 	  or by giving them to
 	  <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>.
@@ -698,8 +829,8 @@ handle_event(_, _, State, Data) ->
 	  override any previous of the same type,
 	  so the last in the containing list wins.
 	  For example, the last
-	  <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso>
-	  overrides any other <c>event_timeout()</c> in the list.
+	  <seealso marker="#type-postpone"><c>postpone()</c></seealso>
+	  overrides any previous <c>postpone()</c> in the list.
 	</p>
 	<taglist>
 	  <tag><c>postpone</c></tag>
@@ -716,6 +847,53 @@ handle_event(_, _, State, Data) ->
 	      as there is no event to postpone in those cases.
 	    </p>
 	  </item>
+	  <tag><c>next_event</c></tag>
+	  <item>
+	    <p>
+	      Stores the specified <c><anno>EventType</anno></c>
+	      and <c><anno>EventContent</anno></c> for insertion after all
+	      actions have been executed.
+	    </p>
+	    <p>
+	      The stored events are inserted in the queue as the next to process
+	      before any already queued events. The order of these stored events
+	      is preserved, so the first <c>next_event</c> in the containing
+	      list becomes the first to process.
+	    </p>
+	    <p>
+	      An event of type
+	      <seealso marker="#type-event_type"><c>internal</c></seealso>
+	      is to be used when you want to reliably distinguish
+	      an event inserted this way from any external event.
+	    </p>
+	  </item>
+	</taglist>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="enter_action"/>
+      <desc>
+	<p>
+	  These state transition actions can be invoked by
+	  returning them from the
+	  <seealso marker="#state callback">state callback</seealso>, from
+	  <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
+	  or by giving them to
+	  <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>.
+	</p>
+	<p>
+	  Actions are executed in the containing list order.
+	</p>
+	<p>
+	  Actions that set
+	  <seealso marker="#type-transition_option">transition options</seealso>
+	  override any previous of the same type,
+	  so the last in the containing list wins.
+	  For example, the last
+	  <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso>
+	  overrides any previous <c>event_timeout()</c> in the list.
+	</p>
+	<taglist>
 	  <tag><c>hibernate</c></tag>
 	  <item>
 	    <p>
@@ -731,7 +909,7 @@ handle_event(_, _, State, Data) ->
 	      Short for <c>{timeout,Timeout,Timeout}</c>, that is,
 	      the time-out message is the time-out time.
 	      This form exists to make the
-	      <seealso marker="#state_function">state function</seealso>
+	      <seealso marker="#state callback">state callback</seealso>
 	      return value <c>{next_state,NextState,NewData,Timeout}</c>
 	      allowed like for <c>gen_fsm</c>'s
 	      <seealso marker="gen_fsm#Module:StateName/2"><c>Module:StateName/2</c></seealso>.
@@ -746,30 +924,13 @@ handle_event(_, _, State, Data) ->
 	      to <c><anno>Time</anno></c> with <c><anno>EventContent</anno></c>.
 	    </p>
 	  </item>
-	  <tag><c>reply_action()</c></tag>
-	  <item>
-	    <p>
-              Replies to a caller.
-	    </p>
-          </item>
-	  <tag><c>next_event</c></tag>
+	  <tag><c>state_timeout</c></tag>
 	  <item>
 	    <p>
-	      Stores the specified <c><anno>EventType</anno></c>
-	      and <c><anno>EventContent</anno></c> for insertion after all
-	      actions have been executed.
-	    </p>
-	    <p>
-	      The stored events are inserted in the queue as the next to process
-	      before any already queued events. The order of these stored events
-	      is preserved, so the first <c>next_event</c> in the containing
-	      list becomes the first to process.
-	    </p>
-	    <p>
-	      An event of type
-	      <seealso marker="#type-event_type"><c>internal</c></seealso>
-	      is to be used when you want to reliably distinguish
-	      an event inserted this way from any external event.
+	      Sets the
+	      <seealso marker="#type-transition_option"><c>transition_option()</c></seealso>
+	      <seealso marker="#type-state_timeout"><c>state_timeout()</c></seealso>
+	      to <c><anno>Time</anno></c> with <c><anno>EventContent</anno></c>.
 	    </p>
 	  </item>
 	</taglist>
@@ -779,39 +940,70 @@ handle_event(_, _, State, Data) ->
       <name name="reply_action"/>
       <desc>
 	<p>
-	  Replies to a caller waiting for a reply in
+	  This state transition action can be invoked by
+	  returning it from the
+	  <seealso marker="#state callback">state callback</seealso>, from
+	  <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
+	  or by giving it to
+	  <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>.
+	</p>
+	<p>
+	  It replies to a caller waiting for a reply in
 	  <seealso marker="#call/2"><c>call/2</c></seealso>.
 	  <c><anno>From</anno></c> must be the term from argument
 	  <seealso marker="#type-event_type"><c>{call,<anno>From</anno>}</c></seealso>
-	  to the
-	  <seealso marker="#state_function">state function</seealso>.
+	  in a call to a
+	  <seealso marker="#state callback">state callback</seealso>.
+	</p>
+	<p>
+	  Note that using this action from 
+	  <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
+	  or
+	  <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>
+	  would be weird on the border of whichcraft
+	  since there has been no earlier call to a
+	  <seealso marker="#state callback">state callback</seealso>
+	  in this server.
 	</p>
       </desc>
     </datatype>
     <datatype>
-      <name name="state_function_result"/>
+      <name name="state_enter_result"/>
       <desc>
+	<p>
+	  <c><anno>State</anno></c> is the current state
+	  and it can not be changed since the state callback
+	  was called with a
+	  <seealso marker="#type-state_enter"><em>state enter call</em></seealso>.
+	</p>
 	<taglist>
 	  <tag><c>next_state</c></tag>
 	  <item>
 	    <p>
 	      The <c>gen_statem</c> does a state transition to
-	      <c><anno>NextStateName</anno></c>
-	      (which can be the same as the current state),
+	      <c><anno>State</anno></c>, which has to be
+	      the current state,
 	      sets <c><anno>NewData</anno></c>,
 	      and executes all <c><anno>Actions</anno></c>.
 	    </p>
 	  </item>
 	</taglist>
-	<p>
-	  All these terms are tuples or atoms and this property
-	  will hold in any future version of <c>gen_statem</c>.
-	</p>
       </desc>
     </datatype>
     <datatype>
-      <name name="handle_event_result"/>
+      <name name="event_handler_result"/>
       <desc>
+	<p>
+	  <c><anno>StateType</anno></c> is
+	  <seealso marker="#type-state_name"><c>state_name()</c></seealso>
+	  if
+	  <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
+	  is <c>state_functions</c>, or
+	  <seealso marker="#type-state"><c>state()</c></seealso>
+	  if
+	  <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
+	  is <c>handle_event_function</c>.
+	</p>
 	<taglist>
 	  <tag><c>next_state</c></tag>
 	  <item>
@@ -824,35 +1016,21 @@ handle_event(_, _, State, Data) ->
 	    </p>
 	  </item>
 	</taglist>
-	<p>
-	  All these terms are tuples or atoms and this property
-	  will hold in any future version of <c>gen_statem</c>.
-	</p>
       </desc>
     </datatype>
     <datatype>
-      <name name="common_state_callback_result"/>
+      <name name="state_callback_result"/>
       <desc>
+	<p>
+	  <c><anno>ActionType</anno></c> is
+	  <seealso marker="#type-enter_action"><c>enter_action()</c></seealso>
+	  if the state callback was called with a
+	  <seealso marker="#type-state_enter"><em>state enter call</em></seealso>
+	  and
+	  <seealso marker="#type-action"><c>action()</c></seealso>
+	  if the state callback was called with an event.
+	</p>
 	<taglist>
-	  <tag><c>stop</c></tag>
-	  <item>
-	    <p>
-	      Terminates the <c>gen_statem</c> by calling
-	      <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso>
-	      with <c>Reason</c> and
-	      <c><anno>NewData</anno></c>, if specified.
-	    </p>
-	  </item>
-	  <tag><c>stop_and_reply</c></tag>
-	  <item>
-	    <p>
-	      Sends all <c><anno>Replies</anno></c>,
-	      then terminates the <c>gen_statem</c> by calling
-	      <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso>
-	      with <c>Reason</c> and
-	      <c><anno>NewData</anno></c>, if specified.
-	    </p>
-	  </item>
 	  <tag><c>keep_state</c></tag>
 	  <item>
 	    <p>
@@ -875,6 +1053,25 @@ handle_event(_, _, State, Data) ->
 	      <c>{next_state,CurrentState,CurrentData,<anno>Actions</anno>}</c>.
 	    </p>
 	  </item>
+	  <tag><c>stop</c></tag>
+	  <item>
+	    <p>
+	      Terminates the <c>gen_statem</c> by calling
+	      <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso>
+	      with <c>Reason</c> and
+	      <c><anno>NewData</anno></c>, if specified.
+	    </p>
+	  </item>
+	  <tag><c>stop_and_reply</c></tag>
+	  <item>
+	    <p>
+	      Sends all <c><anno>Replies</anno></c>,
+	      then terminates the <c>gen_statem</c> by calling
+	      <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso>
+	      with <c>Reason</c> and
+	      <c><anno>NewData</anno></c>, if specified.
+	    </p>
+	  </item>
 	</taglist>
 	<p>
 	  All these terms are tuples or atoms and this property
@@ -896,14 +1093,14 @@ handle_event(_, _, State, Data) ->
 	  by sending a request
 	  and waiting until its reply arrives.
 	  The <c>gen_statem</c> calls the
-	  <seealso marker="#state_function">state function</seealso> with
+	  <seealso marker="#state callback">state callback</seealso> with
 	  <seealso marker="#type-event_type"><c>event_type()</c></seealso>
 	  <c>{call,From}</c> and event content
 	  <c><anno>Request</anno></c>.
 	</p>
 	<p>
 	  A <c><anno>Reply</anno></c> is generated when a
-	  <seealso marker="#state_function">state function</seealso>
+	  <seealso marker="#state callback">state callback</seealso>
 	  returns with
 	  <c>{reply,From,<anno>Reply</anno>}</c> as one
 	  <seealso marker="#type-action"><c>action()</c></seealso>,
@@ -919,18 +1116,40 @@ handle_event(_, _, State, Data) ->
 	</p>
 	<note>
 	  <p>
-	    For <c><anno>Timeout</anno> =/= infinity</c>,
+	    For <c><anno>Timeout</anno> &lt; infinity</c>,
 	    to avoid getting a late reply in the caller's
-	    inbox, this function spawns a proxy process that
+	    inbox if the caller should catch exceptions,
+	    this function spawns a proxy process that
 	    does the call. A late reply gets delivered to the
 	    dead proxy process, hence gets discarded. This is
 	    less efficient than using
-	    <c><anno>Timeout</anno> =:= infinity</c>.
+	    <c><anno>Timeout</anno> == infinity</c>.
 	  </p>
 	</note>
 	<p>
-	  The call can fail, for example, if the <c>gen_statem</c> dies
-	  before or during this function call.
+	  <c><anno>Timeout</anno></c> can also be a tuple
+	  <c>{clean_timeout,<anno>T</anno>}</c> or
+	  <c>{dirty_timeout,<anno>T</anno>}</c>, where
+	  <c><anno>T</anno></c> is the timeout time.
+	  <c>{clean_timeout,<anno>T</anno>}</c> works like
+	  just <c>T</c> described in the note above
+	  and uses a proxy process for <c>T &lt; infinity</c>,
+	  while <c>{dirty_timeout,<anno>T</anno>}</c>
+	  bypasses the proxy process which is more lightweight.
+	</p>
+	<note>
+	  <p>
+	    If you combine catching exceptions from this function
+	    with <c>{dirty_timeout,<anno>T</anno>}</c>
+	    to avoid that the calling process dies when the call
+	    times out, you will have to be prepared to handle
+	    a late reply.
+	    So why not just allow the calling process to die?
+	  </p>
+	</note>
+	<p>
+	  The call can also fail, for example, if the <c>gen_statem</c>
+	  dies before or during this function call.
 	</p>
       </desc>
     </func>
@@ -946,7 +1165,7 @@ handle_event(_, _, State, Data) ->
 	  ignoring if the destination node or <c>gen_statem</c>
 	  does not exist.
 	  The <c>gen_statem</c> calls the
-	  <seealso marker="#state_function">state function</seealso> with
+	  <seealso marker="#state callback">state callback</seealso> with
 	  <seealso marker="#type-event_type"><c>event_type()</c></seealso>
 	  <c>cast</c> and event content
 	  <c><anno>Msg</anno></c>.
@@ -1060,17 +1279,18 @@ handle_event(_, _, State, Data) ->
 	  <seealso marker="#call/2"><c>call/2</c></seealso>
 	  when the reply cannot be defined in
 	  the return value of a
-	  <seealso marker="#state_function">state function</seealso>.
+	  <seealso marker="#state callback">state callback</seealso>.
 	</p>
 	<p>
 	  <c><anno>From</anno></c> must be the term from argument
 	  <seealso marker="#type-event_type"><c>{call,<anno>From</anno>}</c></seealso>
 	  to the
-	  <seealso marker="#state_function">state function</seealso>.
-	  <c><anno>From</anno></c> and <c><anno>Reply</anno></c>
-	  can also be specified using a
-	  <seealso marker="#type-reply_action"><c>reply_action()</c></seealso>
-	  and multiple replies with a list of them.
+	  <seealso marker="#state callback">state callback</seealso>.
+	  A reply or multiple replies canalso be sent
+	  using one or several
+	  <seealso marker="#type-reply_action"><c>reply_action()</c></seealso>s
+	  from a
+	  <seealso marker="#state callback">state callback</seealso>.
 	</p>
 	<note>
 	  <p>
@@ -1266,7 +1486,9 @@ handle_event(_, _, State, Data) ->
       <type>
 	<v>
 	  CallbackMode =
-	  <seealso marker="#type-callback_mode">callback_mode()</seealso>
+	  <seealso marker="#type-callback_mode">callback_mode()</seealso> |
+	  [ <seealso marker="#type-callback_mode">callback_mode()</seealso>
+	  | <seealso marker="#type-state_enter">state_enter()</seealso> ]
 	</v>
       </type>
       <desc>
@@ -1278,8 +1500,9 @@ handle_event(_, _, State, Data) ->
 	  for efficiency reasons, so this function is only called
 	  once after server start and after code change,
 	  but before the first
-	  <seealso marker="#state_function">state function</seealso>
-	  is called.  More occasions may be added in future versions
+	  <seealso marker="#state callback">state callback</seealso>
+	  in the current code version is called.
+	  More occasions may be added in future versions
 	  of <c>gen_statem</c>.
 	</p>
 	<p>
@@ -1291,12 +1514,18 @@ handle_event(_, _, State, Data) ->
 	  <seealso marker="#Module:code_change/4"><c>Module:code_change/4</c></seealso>
 	  returns.
 	</p>
+	<p>
+	  The <c>CallbackMode</c> is either just
+	  <seealso marker="#type-callback_mode"><c>callback_mode()</c></seealso>
+	  or a list containing
+	  <seealso marker="#type-callback_mode"><c>callback_mode()</c></seealso>
+	  and possibly the atom
+	  <seealso marker="#type-state_enter"><c>state_enter</c></seealso>.
+	</p>
 	<note>
 	  <p>
-	    If this function's body does not consist of solely one of two
-	    possible
-	    <seealso marker="#type-callback_mode">atoms</seealso>
-	    the callback module is doing something strange.
+	    If this function's body does not return an inline constant
+	    value the callback module is doing something strange.
 	  </p>
 	</note>
       </desc>
@@ -1416,7 +1645,7 @@ handle_event(_, _, State, Data) ->
 	  The <seealso marker="#type-action"><c>Actions</c></seealso>
 	  are executed when entering the first
 	  <seealso marker="#type-state">state</seealso> just as for a
-	  <seealso marker="#state_function">state function</seealso>.
+	  <seealso marker="#state callback">state callback</seealso>.
 	</p>
 	<p>
 	  If the initialization fails,
@@ -1512,7 +1741,8 @@ handle_event(_, _, State, Data) ->
 	</p>
 	<p>
 	  The function is to return <c>Status</c>, a term that
-          changes the details of the current state and status of
+	  contains the appropriate details
+          of the current state and status of
           the <c>gen_statem</c>. There are no restrictions on the
           form <c>Status</c> can take, but for the
           <seealso marker="sys#get_status/1"><c>sys:get_status/1,2</c></seealso>
@@ -1536,11 +1766,17 @@ handle_event(_, _, State, Data) ->
     </func>
 
     <func>
+      <name>Module:StateName(enter, OldState, Data) ->
+        StateEnterResult(StateName)
+      </name>
       <name>Module:StateName(EventType, EventContent, Data) ->
         StateFunctionResult
       </name>
-      <name>Module:handle_event(EventType, EventContent,
-        State, Data) -> HandleEventResult
+      <name>Module:handle_event(enter, OldState, State, Data) ->
+	StateEnterResult
+      </name>
+      <name>Module:handle_event(EventType, EventContent, State, Data) ->
+	HandleEventResult
       </name>
       <fsummary>Handle an event.</fsummary>
       <type>
@@ -1558,12 +1794,20 @@ handle_event(_, _, State, Data) ->
 	  <seealso marker="#type-data">data()</seealso>
 	</v>
 	<v>
+	  StateEnterResult(StateName) =
+	  <seealso marker="#type-state_enter_result">state_enter_result(StateName)</seealso>
+	</v>
+	<v>
 	  StateFunctionResult =
-	  <seealso marker="#type-state_function_result">state_function_result()</seealso>
+	  <seealso marker="#type-event_handler_result">event_handler_result</seealso>(<seealso marker="#type-state_name">state_name()</seealso>)
+	</v>
+	<v>
+	  StateEnterResult =
+	  <seealso marker="#type-state_enter_result">state_enter_result</seealso>(<seealso marker="#type-state">state()</seealso>)
 	</v>
 	<v>
 	  HandleEventResult =
-	  <seealso marker="#type-handle_event_result">handle_event_result()</seealso>
+	  <seealso marker="#type-event_handler_result">event_handler_result</seealso>(<seealso marker="#type-state">state()</seealso>)
 	</v>
       </type>
       <desc>
@@ -1582,7 +1826,7 @@ handle_event(_, _, State, Data) ->
 	  <seealso marker="#type-event_type"><c>{call,From}</c></seealso>,
 	  the caller waits for a reply. The reply can be sent
 	  from this or from any other
-	  <seealso marker="#state_function">state function</seealso>
+	  <seealso marker="#state callback">state callback</seealso>
 	  by returning with <c>{reply,From,Reply}</c> in
 	  <seealso marker="#type-action"><c>Actions</c></seealso>, in
 	  <seealso marker="#type-reply_action"><c>Replies</c></seealso>,
@@ -1606,6 +1850,24 @@ handle_event(_, _, State, Data) ->
 	  see <seealso marker="#type-action"><c>action()</c></seealso>.
 	</p>
 	<p>
+	  When the <c>gen_statem</c> runs with
+	  <seealso marker="#type-state_enter">state enter calls</seealso>,
+	  these functions are also called with arguments
+	  <c>(enter, OldState, ...)</c> whenever the state changes.
+	  In this case there are some restrictions on the
+	  <seealso marker="#type-enter_action">actions</seealso>
+	  that may be returned:
+	  <seealso marker="#type-postpone"><c>postpone()</c></seealso>
+	  and 
+	  <seealso marker="#type-action"><c>{next_event,_,_}</c></seealso>
+	  are not allowed.
+	  You may also not change states from this call.
+	  Should you return <c>{next_state,NextState, ...}</c>
+	  with <c>NextState =/= State</c> the <c>gen_statem</c> crashes.
+	  You are advised to use <c>{keep_state,...}</c> or
+	  <c>keep_state_and_data</c>.
+	</p>
+	<p>
 	  Note the fact that you can use
 	  <seealso marker="erts:erlang#throw/1"><c>throw</c></seealso>
 	  to return the result, which can be useful.
diff --git a/lib/stdlib/src/gen_statem.erl b/lib/stdlib/src/gen_statem.erl
index 3b3477b282..17d1ebecec 100644
--- a/lib/stdlib/src/gen_statem.erl
+++ b/lib/stdlib/src/gen_statem.erl
@@ -44,15 +44,20 @@
 -export(
    [wakeup_from_hibernate/3]).
 
-%% Type exports for templates
+%% Type exports for templates and callback modules
 -export_type(
    [event_type/0,
-    callback_mode/0,
+    init_result/0,
+    callback_mode_result/0,
     state_function_result/0,
     handle_event_result/0,
+    state_enter_result/1,
+    event_handler_result/1,
+    reply_action/0,
+    enter_action/0,
     action/0]).
 
-%% Fix problem for doc build
+%% Type that is exported just to be documented
 -export_type([transition_option/0]).
 
 %%%==========================================================================
@@ -63,7 +68,7 @@
 	{To :: pid(), Tag :: term()}. % Reply-to specifier for call
 
 -type state() ::
-	state_name() | % For StateName/3 callback functios
+	state_name() | % For StateName/3 callback functions
 	term(). % For handle_event/4 callback function
 
 -type state_name() :: atom().
@@ -72,9 +77,12 @@
 
 -type event_type() ::
 	{'call',From :: from()} | 'cast' |
-	'info' | 'timeout' | 'internal'.
+	'info' | 'timeout' | 'state_timeout' | 'internal'.
 
+-type callback_mode_result() ::
+	callback_mode() | [callback_mode() | state_enter()].
 -type callback_mode() :: 'state_functions' | 'handle_event_function'.
+-type state_enter() :: 'state_enter'.
 
 -type transition_option() ::
 	postpone() | hibernate() | event_timeout().
@@ -89,6 +97,10 @@
 	%% Generate a ('timeout', EventContent, ...) event after Time
 	%% unless some other event is delivered
 	Time :: timeout().
+-type state_timeout() ::
+	%% Generate a ('state_timeout', EventContent, ...) event after Time
+	%% unless the state is changed
+	Time :: timeout().
 
 -type action() ::
 	%% During a state change:
@@ -108,44 +120,67 @@
 	'postpone' |  % Set the postpone option
 	{'postpone', Postpone :: postpone()} |
 	%%
+	%% All 'next_event' events are kept in a list and then
+	%% inserted at state changes so the first in the
+	%% action() list is the first to be delivered.
+	{'next_event', % Insert event as the next to handle
+	 EventType :: event_type(),
+	 EventContent :: term()} |
+	enter_action().
+-type enter_action() ::
 	'hibernate' | % Set the hibernate option
 	{'hibernate', Hibernate :: hibernate()} |
 	%%
 	(Timeout :: event_timeout()) | % {timeout,Timeout}
-	{'timeout', % Set the event timeout option
+	{'timeout', % Set the event_timeout option
 	 Time :: event_timeout(), EventContent :: term()} |
+	{'state_timeout', % Set the state_timeout option
+	 Time :: state_timeout(), EventContent :: term()} |
 	%%
-	reply_action() |
-	%%
-	%% All 'next_event' events are kept in a list and then
-	%% inserted at state changes so the first in the
-	%% action() list is the first to be delivered.
-	{'next_event', % Insert event as the next to handle
-	 EventType :: event_type(),
-	 EventContent :: term()}.
+	reply_action().
 -type reply_action() ::
 	{'reply', % Reply to a caller
 	 From :: from(), Reply :: term()}.
 
+-type init_result() ::
+    {ok, state(), data()} |
+    {ok, state(), data(), [action()] | action()} |
+    'ignore' |
+    {'stop', Reason :: term()}.
+
+%% Old, not advertised
 -type state_function_result() ::
-	{'next_state', % {next_state,NextStateName,NewData,[]}
-	 NextStateName :: state_name(),
+	event_handler_result(state_name()).
+-type handle_event_result() ::
+	event_handler_result(state()).
+%%
+-type state_enter_result(StateType) ::
+	{'next_state', % {next_state,NextState,NewData,[]}
+	 State :: StateType,
 	 NewData :: data()} |
 	{'next_state', % State transition, maybe to the same state
-	 NextStateName :: state_name(),
+	 State :: StateType,
 	 NewData :: data(),
-	 Actions :: [action()] | action()} |
-	common_state_callback_result().
--type handle_event_result() ::
+	 Actions :: [enter_action()] | enter_action()} |
+	state_callback_result(enter_action()).
+-type event_handler_result(StateType) ::
 	{'next_state', % {next_state,NextState,NewData,[]}
-	 NextState :: state(),
+	 NextState :: StateType,
 	 NewData :: data()} |
 	{'next_state', % State transition, maybe to the same state
-	 NextState :: state(),
+	 NextState :: StateType,
 	 NewData :: data(),
 	 Actions :: [action()] | action()} |
-	common_state_callback_result().
--type common_state_callback_result() ::
+	state_callback_result(action()).
+-type state_callback_result(ActionType) ::
+	{'keep_state', % {keep_state,NewData,[]}
+	 NewData :: data()} |
+	{'keep_state', % Keep state, change data
+	 NewData :: data(),
+	 Actions :: [ActionType] | ActionType} |
+	'keep_state_and_data' | % {keep_state_and_data,[]}
+	{'keep_state_and_data', % Keep state and data -> only actions
+	 Actions :: [ActionType] | ActionType} |
 	'stop' | % {stop,normal}
 	{'stop', % Stop the server
 	 Reason :: term()} |
@@ -158,32 +193,20 @@
 	{'stop_and_reply', % Reply then stop the server
 	 Reason :: term(),
 	 Replies :: [reply_action()] | reply_action(),
-	 NewData :: data()} |
-	{'keep_state', % {keep_state,NewData,[]}
-	 NewData :: data()} |
-	{'keep_state', % Keep state, change data
-	 NewData :: data(),
-	 Actions :: [action()] | action()} |
-	'keep_state_and_data' | % {keep_state_and_data,[]}
-	{'keep_state_and_data', % Keep state and data -> only actions
-	 Actions :: [action()] | action()}.
+	 NewData :: data()}.
 
 
 %% The state machine init function.  It is called only once and
 %% the server is not running until this function has returned
 %% an {ok, ...} tuple.  Thereafter the state callbacks are called
 %% for all events to this server.
--callback init(Args :: term()) ->
-    {ok, state(), data()} |
-    {ok, state(), data(), [action()] | action()} |
-    'ignore' |
-    {'stop', Reason :: term()}.
+-callback init(Args :: term()) -> init_result().
 
 %% This callback shall return the callback mode of the callback module.
 %%
 %% It is called once after init/0 and code_change/4 but before
 %% the first state callback StateName/3 or handle_event/4.
--callback callback_mode() -> callback_mode().
+-callback callback_mode() -> callback_mode_result().
 
 %% Example state callback for StateName = 'state_name'
 %% when callback_mode() =:= state_functions.
@@ -194,19 +217,28 @@
 %% StateName/3 callbacks and terminate/3, so the state name
 %% 'terminate' is unusable in this mode.
 -callback state_name(
-	    event_type(),
+	    'enter',
+	    OldStateName :: state_name(),
+	    Data :: data()) ->
+    state_enter_result('state_name');
+           (event_type(),
 	    EventContent :: term(),
 	    Data :: data()) ->
-    state_function_result().
+    event_handler_result(state_name()).
 %%
 %% State callback for all states
 %% when callback_mode() =:= handle_event_function.
 -callback handle_event(
-	    event_type(),
+	    'enter',
+	    OldState :: state(),
+	    State :: state(), % Current state
+	    Data :: data()) ->
+    state_enter_result(state());
+           (event_type(),
 	    EventContent :: term(),
 	    State :: state(), % Current state
 	    Data :: data()) ->
-    handle_event_result().
+    event_handler_result(state()).
 
 %% Clean up before the server terminates.
 -callback terminate(
@@ -385,53 +417,79 @@ call(ServerRef, Request) ->
 -spec call(
 	ServerRef :: server_ref(),
 	Request :: term(),
-	Timeout :: timeout()) ->
+	Timeout ::
+	  timeout() |
+	  {'clean_timeout',T :: timeout()} |
+	  {'dirty_timeout',T :: timeout()}) ->
 		  Reply :: term().
-call(ServerRef, Request, infinity) ->
-    try gen:call(ServerRef, '$gen_call', Request, infinity) of
-	{ok,Reply} ->
-	    Reply
-    catch
-	Class:Reason ->
-	    erlang:raise(
-	      Class,
-	      {Reason,{?MODULE,call,[ServerRef,Request,infinity]}},
-	      erlang:get_stacktrace())
-    end;
 call(ServerRef, Request, Timeout) ->
-    %% Call server through proxy process to dodge any late reply
-    Ref = make_ref(),
-    Self = self(),
-    Pid = spawn(
-	    fun () ->
-		    Self !
-			try gen:call(
-			      ServerRef, '$gen_call', Request, Timeout) of
-			    Result ->
-				{Ref,Result}
-			catch Class:Reason ->
-				{Ref,Class,Reason,erlang:get_stacktrace()}
-			end
-	    end),
-    Mref = monitor(process, Pid),
-    receive
-	{Ref,Result} ->
-	    demonitor(Mref, [flush]),
-	    case Result of
+    case parse_timeout(Timeout) of
+	{dirty_timeout,T} ->
+	    try gen:call(ServerRef, '$gen_call', Request, T) of
 		{ok,Reply} ->
 		    Reply
+	    catch
+		Class:Reason ->
+		    erlang:raise(
+		      Class,
+		      {Reason,{?MODULE,call,[ServerRef,Request,Timeout]}},
+		      erlang:get_stacktrace())
+	    end;
+	{clean_timeout,T} ->
+	    %% Call server through proxy process to dodge any late reply
+	    Ref = make_ref(),
+	    Self = self(),
+	    Pid = spawn(
+		    fun () ->
+			    Self !
+				try gen:call(
+				      ServerRef, '$gen_call', Request, T) of
+				    Result ->
+					{Ref,Result}
+				catch Class:Reason ->
+					{Ref,Class,Reason,
+					 erlang:get_stacktrace()}
+				end
+		    end),
+	    Mref = monitor(process, Pid),
+	    receive
+		{Ref,Result} ->
+		    demonitor(Mref, [flush]),
+		    case Result of
+			{ok,Reply} ->
+			    Reply
+		    end;
+		{Ref,Class,Reason,Stacktrace} ->
+		    demonitor(Mref, [flush]),
+		    erlang:raise(
+		      Class,
+		      {Reason,{?MODULE,call,[ServerRef,Request,Timeout]}},
+		      Stacktrace);
+		{'DOWN',Mref,_,_,Reason} ->
+		    %% There is a theoretical possibility that the
+		    %% proxy process gets killed between try--of and !
+		    %% so this clause is in case of that
+		    exit(Reason)
 	    end;
-	{Ref,Class,Reason,Stacktrace} ->
-	    demonitor(Mref, [flush]),
-	    erlang:raise(
-	      Class,
-	      {Reason,{?MODULE,call,[ServerRef,Request,Timeout]}},
-	      Stacktrace);
-	{'DOWN',Mref,_,_,Reason} ->
-	    %% There is a theoretical possibility that the
-	    %% proxy process gets killed between try--of and !
-	    %% so this clause is in case of that
-	    exit(Reason)
+	Error when is_atom(Error) ->
+	    erlang:error(Error, [ServerRef,Request,Timeout])
+    end.
+
+parse_timeout(Timeout) ->
+    case Timeout of
+	{clean_timeout,infinity} ->
+	    {dirty_timeout,infinity};
+	{clean_timeout,_} ->
+	    Timeout;
+	{dirty_timeout,_} ->
+	    Timeout;
+	{_,_} ->
+	    %% Be nice and throw a badarg for speling errors
+	    badarg;
+	infinity ->
+	    {dirty_timeout,infinity};
+	T ->
+	    {clean_timeout,T}
     end.
 
 %% Reply from a state machine callback to whom awaits in call/2
@@ -517,8 +575,9 @@ enter(Module, Opts, State, Data, Server, Actions, Parent) ->
     %% The values should already have been type checked
     Name = gen:get_proc_name(Server),
     Debug = gen:debug_options(Name, Opts),
-    P = Events = [],
-    Event = {internal,initial_state},
+    Events = [],
+    P = [],
+    Event = {internal,init_state},
     %% We enforce {postpone,false} to ensure that
     %% our fake Event gets discarded, thought it might get logged
     NewActions =
@@ -530,19 +589,31 @@ enter(Module, Opts, State, Data, Server, Actions, Parent) ->
 	end,
     S =	#{
       callback_mode => undefined,
+      state_enter => false,
       module => Module,
       name => Name,
-      %% All fields below will be replaced according to the arguments to
-      %% loop_event_actions/10 when it finally loops back to loop/3
       state => State,
       data => Data,
       postponed => P,
-      hibernate => false,
-      timer => undefined},
+      %% The rest of the fields are set from to the arguments to
+      %% loop_event_actions/9 when it finally loops back to loop/3
+      %% in loop_events_done/9
+      %%
+      %% Marker for initial state, cleared immediately when used
+      init_state => true
+     },
     NewDebug = sys_debug(Debug, S, State, {enter,Event,State}),
-    loop_event_actions(
-      Parent, NewDebug, S, Events,
-      State, Data, P, Event, State, NewActions).
+    case call_callback_mode(S) of
+	{ok,NewS} ->
+	    StateTimer = undefined,
+	    loop_event_actions(
+	      Parent, NewDebug, NewS, StateTimer,
+	      Events, Event, State, Data, NewActions);
+	{Class,Reason,Stacktrace} ->
+	    terminate(
+	      Class, Reason, Stacktrace,
+	      NewDebug, S, [Event|Events])
+    end.
 
 %%%==========================================================================
 %%%  gen callbacks
@@ -563,7 +634,9 @@ init_it(Starter, Parent, ServerRef, Module, Args, Opts) ->
 	    proc_lib:init_ack(Starter, {error,Reason}),
 	    error_info(
 	      Class, Reason, Stacktrace,
-	      #{name => Name, callback_mode => undefined},
+	      #{name => Name,
+		callback_mode => undefined,
+		state_enter => false},
 	      [], [], undefined),
 	    erlang:raise(Class, Reason, Stacktrace)
     end.
@@ -594,7 +667,9 @@ init_result(Starter, Parent, ServerRef, Module, Result, Opts) ->
 	    proc_lib:init_ack(Starter, {error,Error}),
 	    error_info(
 	      error, Error, ?STACKTRACE(),
-	      #{name => Name, callback_mode => undefined},
+	      #{name => Name,
+		callback_mode => undefined,
+		state_enter => false},
 	      [], [], undefined),
 	    exit(Error)
     end.
@@ -605,12 +680,10 @@ init_result(Starter, Parent, ServerRef, Module, Result, Opts) ->
 system_continue(Parent, Debug, S) ->
     loop(Parent, Debug, S).
 
-system_terminate(
-  Reason, _Parent, Debug,
-  #{state := State, data := Data, postponed := P} = S) ->
+system_terminate(Reason, _Parent, Debug, S) ->
     terminate(
       exit, Reason, ?STACKTRACE(),
-      Debug, S, [], State, Data, P).
+      Debug, S, []).
 
 system_code_change(
   #{module := Module,
@@ -647,7 +720,7 @@ system_replace_state(
 format_status(
   Opt,
   [PDict,SysState,Parent,Debug,
-   #{name := Name, postponed := P, state := State, data := Data} = S]) ->
+   #{name := Name, postponed := P} = S]) ->
     Header = gen:format_status_header("Status for state machine", Name),
     Log = sys:get_debug(log, Debug, []),
     [{header,Header},
@@ -656,7 +729,7 @@ format_status(
        {"Parent",Parent},
        {"Logged Events",Log},
        {"Postponed",P}]} |
-     case format_status(Opt, PDict, S, State, Data) of
+     case format_status(Opt, PDict, S) of
 	 L when is_list(L) -> L;
 	 T -> [T]
      end].
@@ -732,7 +805,8 @@ loop(Parent, Debug, #{hibernate := Hibernate} = S) ->
     end.
 
 %% Entry point for wakeup_from_hibernate/3
-loop_receive(Parent, Debug, #{timer := Timer} = S) ->
+loop_receive(
+  Parent, Debug, #{timer := Timer, state_timer := StateTimer} = S) ->
     receive
 	Msg ->
 	    case Msg of
@@ -743,34 +817,23 @@ loop_receive(Parent, Debug, #{timer := Timer} = S) ->
 		    sys:handle_system_msg(
 		      Req, Pid, Parent, ?MODULE, Debug, S, Hibernate);
 		{'EXIT',Parent,Reason} = EXIT ->
-		    #{state := State, data := Data, postponed := P} = S,
 		    %% EXIT is not a 2-tuple and therefore
 		    %% not an event and has no event_type(),
 		    %% but this will stand out in the crash report...
 		    terminate(
-		      exit, Reason, ?STACKTRACE(),
-		      Debug, S, [EXIT], State, Data, P);
-		{timeout,Timer,Content} when Timer =/= undefined ->
+		      exit, Reason, ?STACKTRACE(), Debug, S, [EXIT]);
+		{timeout,Timer,Content}
+		  when Timer =/= undefined ->
 		    loop_receive_result(
-		      Parent, Debug, S, {timeout,Content});
+		      Parent, Debug, S, StateTimer,
+		      {timeout,Content});
+		{timeout,StateTimer,Content}
+		  when StateTimer =/= undefined ->
+		    loop_receive_result(
+		      Parent, Debug, S, undefined,
+		      {state_timeout,Content});
 		_ ->
-		    %% Cancel Timer if running
-		    case Timer of
-			undefined ->
-			    ok;
-			_ ->
-			    case erlang:cancel_timer(Timer) of
-				TimeLeft when is_integer(TimeLeft) ->
-				    ok;
-				false ->
-				    receive
-					{timeout,Timer,_} ->
-					    ok
-				    after 0 ->
-					    ok
-				    end
-			    end
-		    end,
+		    cancel_timer(Timer),
 		    Event =
 			case Msg of
 			    {'$gen_call',From,Request} ->
@@ -780,112 +843,185 @@ loop_receive(Parent, Debug, #{timer := Timer} = S) ->
 			    _ ->
 				{info,Msg}
 			end,
-		    loop_receive_result(Parent, Debug, S, Event)
+		    loop_receive_result(
+		      Parent, Debug, S, StateTimer, Event)
 	    end
     end.
 
-loop_receive_result(
-  Parent, Debug,
-  #{state := State,
-    data := Data,
-    postponed := P} = S,
-  Event) ->
-    %% The engine state map S is now dismantled
-    %% and will not be restored until we return to loop/3.
-    %%
-    %% The fields 'callback_mode', 'module', and 'name' are still valid.
-    %% The fields 'state', 'data', and 'postponed' are held in arguments.
-    %% The fields 'timer' and 'hibernate' will be recalculated.
+loop_receive_result(Parent, Debug, #{state := State} = S, StateTimer, Event) ->
+    %% The fields 'timer', 'state_timer' and 'hibernate'
+    %% are now invalid in state map S - they will be recalculated
+    %% and restored when we return to loop/3
     %%
     NewDebug = sys_debug(Debug, S, State, {in,Event}),
     %% Here the queue of not yet handled events is created
     Events = [],
     Hibernate = false,
-    loop_event(
-      Parent, NewDebug, S, Events, State, Data, P, Event, Hibernate).
+    loop_event(Parent, NewDebug, S, StateTimer, Events, Event, Hibernate).
 
 %% Process the event queue, or if it is empty
 %% loop back to loop/3 to receive a new event
 loop_events(
-  Parent, Debug, S, [Event|Events],
-  State, Data, P, Hibernate, _Timeout) ->
+  Parent, Debug, S, StateTimeout,
+  [Event|Events], _Timeout, State, Data, P, Hibernate) ->
     %%
-    %% If there was a state timer requested we just ignore that
+    %% If there was an event timer requested we just ignore that
     %% since we have events to handle which cancels the timer
     loop_event(
-      Parent, Debug, S, Events, State, Data, P, Event, Hibernate);
+      Parent, Debug, S, StateTimeout,
+      Events, Event, State, Data, P, Hibernate);
 loop_events(
-  Parent, Debug, S, [],
-  State, Data, P, Hibernate, Timeout) ->
+  Parent, Debug, S, {state_timeout,Time,EventContent},
+  [] = Events, Timeout, State, Data, P, Hibernate) ->
+    if
+	Time =:= 0 ->
+	    %% Simulate an immediate timeout
+	    %% so we do not get the timeout message
+	    %% after any received event
+	    %% 
+	    %% This faked event will cancel
+	    %& any not yet started event timer
+	    Event = {state_timeout,EventContent},
+	    StateTimer = undefined,
+	    loop_event(
+	      Parent, Debug, S, StateTimer,
+	      Events, Event, State, Data, P, Hibernate);
+	true ->
+	    StateTimer = erlang:start_timer(Time, self(), EventContent),
+	    loop_events(
+	      Parent, Debug, S, StateTimer,
+	      Events, Timeout, State, Data, P, Hibernate)
+    end;
+loop_events(
+  Parent, Debug, S, StateTimer,
+  [] = Events, Timeout, State, Data, P, Hibernate) ->
     case Timeout of
 	{timeout,0,EventContent} ->
-	    %% Immediate timeout - simulate it
+	    %% Simulate an immediate timeout
 	    %% so we do not get the timeout message
 	    %% after any received event
+	    %% 
+	    Event = {timeout,EventContent},
 	    loop_event(
-	      Parent, Debug, S, [],
-	      State, Data, P, {timeout,EventContent}, Hibernate);
+	      Parent, Debug, S, StateTimer,
+	      Events, Event, State, Data, P, Hibernate);
 	{timeout,Time,EventContent} ->
-	    %% Actually start a timer
 	    Timer = erlang:start_timer(Time, self(), EventContent),
 	    loop_events_done(
-	      Parent, Debug, S, Timer, State, Data, P, Hibernate);
+	      Parent, Debug, S, StateTimer,
+	      State, Data, P, Hibernate, Timer);
 	undefined ->
-	    %% No state timeout has been requested
+	    %% No event timeout has been requested
 	    Timer = undefined,
 	    loop_events_done(
-	      Parent, Debug, S, Timer, State, Data, P, Hibernate)
+	      Parent, Debug, S, StateTimer,
+	      State, Data, P, Hibernate, Timer)
     end.
-%%
-loop_events_done(Parent, Debug, S, Timer, State, Data, P, Hibernate) ->
+
+%% Back to the top
+loop_events_done(
+  Parent, Debug, S, StateTimer,
+  State, Data, P, Hibernate, Timer) ->
     NewS =
 	S#{
 	  state := State,
 	  data := Data,
 	  postponed := P,
-	  hibernate := Hibernate,
-	  timer := Timer},
+	  hibernate => Hibernate,
+	  timer => Timer,
+	  state_timer => StateTimer},
     loop(Parent, Debug, NewS).
 
-loop_event(
-  Parent, Debug,
+
+
+call_callback_mode(#{module := Module} = S) ->
+    try Module:callback_mode() of
+	CallbackMode ->
+	    callback_mode_result(S, CallbackMode)
+    catch
+	CallbackMode ->
+	    callback_mode_result(S, CallbackMode);
+	error:undef ->
+	    %% Process undef to check for the simple mistake
+	    %% of calling a nonexistent state function
+	    %% to make the undef more precise
+	    case erlang:get_stacktrace() of
+		[{Module,callback_mode,[]=Args,_}
+		 |Stacktrace] ->
+		    {error,
+		     {undef_callback,{Module,callback_mode,Args}},
+		     Stacktrace};
+		Stacktrace ->
+		    {error,undef,Stacktrace}
+	    end;
+	Class:Reason ->
+	    {Class,Reason,erlang:get_stacktrace()}
+    end.
+
+callback_mode_result(S, CallbackMode) ->
+    case
+	parse_callback_mode(
+	  if
+	      is_atom(CallbackMode) ->
+		  [CallbackMode];
+	      true ->
+		  CallbackMode
+	  end, undefined, false)
+    of
+	{undefined,_} ->
+	    {error,
+	     {bad_return_from_callback_mode,CallbackMode},
+	     ?STACKTRACE()};
+	{CBMode,StateEnter} ->
+	    {ok,
+	     S#{
+	       callback_mode := CBMode,
+	       state_enter := StateEnter}}
+    end.
+
+parse_callback_mode([], CBMode, StateEnter) ->
+    {CBMode,StateEnter};
+parse_callback_mode([H|T], CBMode, StateEnter) ->
+    case callback_mode(H) of
+	true ->
+	    parse_callback_mode(T, H, StateEnter);
+	false ->
+	    case H of
+		state_enter ->
+		    parse_callback_mode(T, CBMode, true);
+		_ ->
+		    {undefined,StateEnter}
+	    end
+    end;
+parse_callback_mode(_, _CBMode, StateEnter) ->
+    {undefined,StateEnter}.
+
+call_state_function(
+  #{callback_mode := undefined} = S,
+  Type, Content, State, Data) ->
+    case call_callback_mode(S) of
+	{ok,NewS} ->
+	    call_state_function(NewS, Type, Content, State, Data);
+	Error ->
+	    Error
+    end;
+call_state_function(
   #{callback_mode := CallbackMode,
     module := Module} = S,
-  Events,
-  State, Data, P, {Type,Content} = Event, Hibernate) ->
-    %%
-    %% If Hibernate is true here it can only be
-    %% because it was set from an event action
-    %% and we did not go into hibernation since there
-    %% were events in queue, so we do what the user
-    %% might depend on i.e collect garbage which
-    %% would have happened if we actually hibernated
-    %% and immediately was awakened
-    Hibernate andalso garbage_collect(),
-    %%
+  Type, Content, State, Data) ->
     try
 	case CallbackMode of
-	    undefined ->
-		Module:callback_mode();
 	    state_functions ->
 		erlang:apply(Module, State, [Type,Content,Data]);
 	    handle_event_function ->
 		Module:handle_event(Type, Content, State, Data)
 	end
     of
-	Result when CallbackMode =:= undefined ->
-	    loop_event_callback_mode(
-	      Parent, Debug, S, Events, State, Data, P, Event, Result);
 	Result ->
-	    loop_event_result(
-	      Parent, Debug, S, Events, State, Data, P, Event, Result)
+	    {ok,Result,S}
     catch
-	Result when CallbackMode =:= undefined ->
-	    loop_event_callback_mode(
-	      Parent, Debug, S, Events, State, Data, P, Event, Result);
 	Result ->
-	    loop_event_result(
-	      Parent, Debug, S, Events, State, Data, P, Event, Result);
+	    {ok,Result,S};
 	error:badarg ->
 	    case erlang:get_stacktrace() of
 		[{erlang,apply,
@@ -895,329 +1031,425 @@ loop_event(
 		  when CallbackMode =:= state_functions ->
 		    %% We get here e.g if apply fails
 		    %% due to State not being an atom
-		    terminate(
-		      error,
-		      {undef_state_function,{Module,State,Args}},
-		      Stacktrace,
-		      Debug, S, [Event|Events], State, Data, P);
+		    {error,
+		     {undef_state_function,{Module,State,Args}},
+		     Stacktrace};
 		Stacktrace ->
-		    terminate(
-		      error, badarg, Stacktrace,
-		      Debug, S, [Event|Events], State, Data, P)
+		    {error,badarg,Stacktrace}
 	    end;
 	error:undef ->
 	    %% Process undef to check for the simple mistake
 	    %% of calling a nonexistent state function
 	    %% to make the undef more precise
 	    case erlang:get_stacktrace() of
-		[{Module,callback_mode,[]=Args,_}
-		 |Stacktrace]
-		  when CallbackMode =:= undefined ->
-		    terminate(
-		      error,
-		      {undef_callback,{Module,callback_mode,Args}},
-		      Stacktrace,
-		      Debug, S, [Event|Events], State, Data, P);
 		[{Module,State,[Type,Content,Data]=Args,_}
 		 |Stacktrace]
 		  when CallbackMode =:= state_functions ->
-		    terminate(
-		      error,
-		      {undef_state_function,{Module,State,Args}},
-		      Stacktrace,
-		      Debug, S, [Event|Events], State, Data, P);
+		    {error,
+		     {undef_state_function,{Module,State,Args}},
+		     Stacktrace};
 		[{Module,handle_event,[Type,Content,State,Data]=Args,_}
 		 |Stacktrace]
 		  when CallbackMode =:= handle_event_function ->
-		    terminate(
-		      error,
-		      {undef_state_function,{Module,handle_event,Args}},
-		      Stacktrace,
-		      Debug, S, [Event|Events], State, Data, P);
+		    {error,
+		     {undef_state_function,{Module,handle_event,Args}},
+		     Stacktrace};
 		Stacktrace ->
-		    terminate(
-		      error, undef, Stacktrace,
-		      Debug, S, [Event|Events], State, Data, P)
+		    {error,undef,Stacktrace}
 	    end;
 	Class:Reason ->
-	    Stacktrace = erlang:get_stacktrace(),
-	    terminate(
-	      Class, Reason, Stacktrace,
-	      Debug, S, [Event|Events], State, Data, P)
+	    {Class,Reason,erlang:get_stacktrace()}
     end.
 
-%% Interpret callback_mode() result
-loop_event_callback_mode(
-  Parent, Debug, S, Events, State, Data, P, Event, CallbackMode) ->
-    case callback_mode(CallbackMode) of
-	true ->
-	    Hibernate = false, % We have already GC:ed recently
-	    loop_event(
-	      Parent, Debug,
-	      S#{callback_mode := CallbackMode},
-	      Events,
-	      State, Data, P, Event, Hibernate);
-	false ->
+%% Update S and continue
+loop_event(
+  Parent, Debug, S, StateTimer,
+  Events, Event, State, Data, P, Hibernate) ->
+    NewS =
+	S#{
+	  state := State,
+	  data := Data,
+	  postponed := P},
+    loop_event(Parent, Debug, NewS, StateTimer, Events, Event, Hibernate).
+
+loop_event(
+  Parent, Debug, #{state := State, data := Data} = S, StateTimer,
+  Events, {Type,Content} = Event, Hibernate) ->
+    %%
+    %% If Hibernate is true here it can only be
+    %% because it was set from an event action
+    %% and we did not go into hibernation since there
+    %% were events in queue, so we do what the user
+    %% might rely on i.e collect garbage which
+    %% would have happened if we actually hibernated
+    %% and immediately was awakened
+    Hibernate andalso garbage_collect(),
+    case call_state_function(S, Type, Content, State, Data) of
+	{ok,Result,NewS} ->
+	    {NewData,NextState,Actions} =
+		parse_event_result(
+		  true, Debug, NewS, Result,
+		  Events, Event, State, Data),
+	    loop_event_actions(
+	      Parent, Debug, S, StateTimer,
+	      Events, Event, NextState, NewData, Actions);
+	{Class,Reason,Stacktrace} ->
 	    terminate(
-	      error,
-	      {bad_return_from_callback_mode,CallbackMode},
-	      ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, Data, P)
+	      Class, Reason, Stacktrace, Debug, S, [Event|Events])
     end.
 
 %% Interpret all callback return variants
-loop_event_result(
-  Parent, Debug, S, Events, State, Data, P, Event, Result) ->
+parse_event_result(
+  AllowStateChange, Debug, S, Result, Events, Event, State, Data) ->
     case Result of
 	stop ->
 	    terminate(
-	      exit, normal, ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, Data, P);
+	      exit, normal, ?STACKTRACE(), Debug, S, [Event|Events]);
 	{stop,Reason} ->
 	    terminate(
-	      exit, Reason, ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, Data, P);
+	      exit, Reason, ?STACKTRACE(), Debug, S, [Event|Events]);
 	{stop,Reason,NewData} ->
 	    terminate(
 	      exit, Reason, ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, NewData, P);
+	      Debug, S#{data := NewData}, [Event|Events]);
 	{stop_and_reply,Reason,Replies} ->
 	    Q = [Event|Events],
 	    reply_then_terminate(
 	      exit, Reason, ?STACKTRACE(),
-	      Debug, S, Q, State, Data, P, Replies);
+	      Debug, S, Q, Replies);
 	{stop_and_reply,Reason,Replies,NewData} ->
 	    Q = [Event|Events],
 	    reply_then_terminate(
 	      exit, Reason, ?STACKTRACE(),
-	      Debug, S, Q, State, NewData, P, Replies);
-	{next_state,NextState,NewData} ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, []);
-	{next_state,NextState,NewData,Actions} ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions);
+	      Debug, S#{data := NewData}, Q, Replies);
+	{next_state,State,NewData} ->
+	    {NewData,State,[]};
+	{next_state,NextState,NewData} when AllowStateChange ->
+	    {NewData,NextState,[]};
+	{next_state,State,NewData,Actions} ->
+	    {NewData,State,Actions};
+	{next_state,NextState,NewData,Actions} when AllowStateChange ->
+	    {NewData,NextState,Actions};
 	{keep_state,NewData} ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, State, []);
+	    {NewData,State,[]};
 	{keep_state,NewData,Actions} ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, State, Actions);
+	    {NewData,State,Actions};
 	keep_state_and_data ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, Data, P, Event, State, []);
+	    {Data,State,[]};
 	{keep_state_and_data,Actions} ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, Data, P, Event, State, Actions);
+	    {Data,State,Actions};
 	_ ->
 	    terminate(
 	      error,
 	      {bad_return_from_state_function,Result},
 	      ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, Data, P)
+	      Debug, S, [Event|Events])
     end.
 
-loop_event_actions(
-  Parent, Debug, S, Events, State, NewData, P, Event, NextState, Actions) ->
-    Postpone = false, % Shall we postpone this event; boolean()
+parse_enter_actions(
+  Debug, S, State, Actions,
+  Hibernate, Timeout, StateTimeout) ->
+    Postpone = forbidden,
+    NextEvents = forbidden,
+    parse_actions(
+      Debug, S, State, listify(Actions),
+      Hibernate, Timeout, StateTimeout, Postpone, NextEvents).
+    
+parse_actions(Debug, S, State, Actions) ->
     Hibernate = false,
     Timeout = undefined,
+    StateTimeout = undefined,
+    Postpone = false,
     NextEvents = [],
-    loop_event_actions(
-      Parent, Debug, S, Events, State, NewData, P, Event, NextState,
-      if
-	  is_list(Actions) ->
-	      Actions;
-	  true ->
-	      [Actions]
-      end,
-      Postpone, Hibernate, Timeout, NextEvents).
+    parse_actions(
+      Debug, S, State, listify(Actions),
+      Hibernate, Timeout, StateTimeout, Postpone, NextEvents).
 %%
-%% Process all actions
-loop_event_actions(
-  Parent, Debug, S, Events,
-  State, NewData, P, Event, NextState, [Action|Actions],
-  Postpone, Hibernate, Timeout, NextEvents) ->
+parse_actions(
+  Debug, _S, _State, [],
+  Hibernate, Timeout, StateTimeout, Postpone, NextEvents) ->
+    {ok,Debug,Hibernate,Timeout,StateTimeout,Postpone,NextEvents};
+parse_actions(
+  Debug, S, State, [Action|Actions],
+  Hibernate, Timeout, StateTimeout, Postpone, NextEvents) ->
     case Action of
 	%% Actual actions
 	{reply,From,Reply} ->
 	    case from(From) of
 		true ->
 		    NewDebug = do_reply(Debug, S, State, From, Reply),
-		    loop_event_actions(
-		      Parent, NewDebug, S, Events,
-		      State, NewData, P, Event, NextState, Actions,
-		      Postpone, Hibernate, Timeout, NextEvents);
+		    parse_actions(
+		      NewDebug, S, State, Actions,
+		      Hibernate, Timeout, StateTimeout,
+		      Postpone, NextEvents);
 		false ->
-		    terminate(
-		      error,
-		      {bad_action_from_state_function,Action},
-		      ?STACKTRACE(),
-		      Debug, S, [Event|Events], State, NewData, P)
-	    end;
-	{next_event,Type,Content} ->
-	    case event_type(Type) of
-		true ->
-		    NewDebug =
-			sys_debug(Debug, S, State, {in,{Type,Content}}),
-		    loop_event_actions(
-		      Parent, NewDebug, S, Events,
-		      State, NewData, P, Event, NextState, Actions,
-		      Postpone, Hibernate, Timeout,
-		      [{Type,Content}|NextEvents]);
-		false ->
-		    terminate(
-		      error,
-		      {bad_action_from_state_function,Action},
-		      ?STACKTRACE(),
-		      Debug, S, [Event|Events], State, NewData, P)
+		    {error,
+		     {bad_action_from_state_function,Action},
+		     ?STACKTRACE()}
 	    end;
 	%% Actions that set options
-	{postpone,NewPostpone} when is_boolean(NewPostpone) ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      NewPostpone, Hibernate, Timeout, NextEvents);
-	{postpone,_} ->
-	    terminate(
-	      error,
-	      {bad_action_from_state_function,Action},
-	      ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, NewData, P);
-	postpone ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      true, Hibernate, Timeout, NextEvents);
 	{hibernate,NewHibernate} when is_boolean(NewHibernate) ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      Postpone, NewHibernate, Timeout, NextEvents);
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      NewHibernate, Timeout, StateTimeout, Postpone, NextEvents);
 	{hibernate,_} ->
-	    terminate(
-	      error,
-	      {bad_action_from_state_function,Action},
-	      ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, NewData, P);
+	    {error,
+	     {bad_action_from_state_function,Action},
+	     ?STACKTRACE()};
 	hibernate ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      Postpone, true, Timeout, NextEvents);
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      true, Timeout, StateTimeout, Postpone, NextEvents);
+	{state_timeout,Time,_} = NewStateTimeout
+	  when is_integer(Time), Time >= 0;
+	       Time =:= infinity ->
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, Timeout, NewStateTimeout, Postpone, NextEvents);
+	{state_timeout,_,_} ->
+	    {error,
+	     {bad_action_from_state_function,Action},
+	     ?STACKTRACE()};
 	{timeout,infinity,_} -> % Clear timer - it will never trigger
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      Postpone, Hibernate, undefined, NextEvents);
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, undefined, StateTimeout, Postpone, NextEvents);
 	{timeout,Time,_} = NewTimeout when is_integer(Time), Time >= 0 ->
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      Postpone, Hibernate, NewTimeout, NextEvents);
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, NewTimeout, StateTimeout, Postpone, NextEvents);
 	{timeout,_,_} ->
-	    terminate(
-	      error,
-	      {bad_action_from_state_function,Action},
-	      ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, NewData, P);
+	    {error,
+	     {bad_action_from_state_function,Action},
+	     ?STACKTRACE()};
 	infinity -> % Clear timer - it will never trigger
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      Postpone, Hibernate, undefined, NextEvents);
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, undefined, StateTimeout, Postpone, NextEvents);
 	Time when is_integer(Time), Time >= 0 ->
 	    NewTimeout = {timeout,Time,Time},
-	    loop_event_actions(
-	      Parent, Debug, S, Events,
-	      State, NewData, P, Event, NextState, Actions,
-	      Postpone, Hibernate, NewTimeout, NextEvents);
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, NewTimeout, StateTimeout, Postpone, NextEvents);
+	{postpone,NewPostpone}
+	  when is_boolean(NewPostpone), Postpone =/= forbidden ->
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, Timeout, StateTimeout, NewPostpone, NextEvents);
+	{postpone,_} ->
+	    {error,
+	     {bad_action_from_state_function,Action},
+	     ?STACKTRACE()};
+	postpone when Postpone =/= forbidden ->
+	    parse_actions(
+	      Debug, S, State, Actions,
+	      Hibernate, Timeout, StateTimeout, true, NextEvents);
+	{next_event,Type,Content} ->
+	    case event_type(Type) of
+		true when NextEvents =/= forbidden ->
+		    NewDebug =
+			sys_debug(Debug, S, State, {in,{Type,Content}}),
+		    parse_actions(
+		      NewDebug, S, State, Actions,
+		      Hibernate, Timeout, StateTimeout,
+		      Postpone, [{Type,Content}|NextEvents]);
+		_ ->
+		    {error,
+		     {bad_action_from_state_function,Action},
+		     ?STACKTRACE()}
+	    end;
 	_ ->
-	    terminate(
-	      error,
-	      {bad_action_from_state_function,Action},
-	      ?STACKTRACE(),
-	      Debug, S, [Event|Events], State, NewData, P)
-    end;
-%%
-%% End of actions list
+	    {error,
+	     {bad_action_from_state_function,Action},
+	     ?STACKTRACE()}
+    end.
+
 loop_event_actions(
-  Parent, Debug, S, Events,
-  State, NewData, P0, Event, NextState, [],
-  Postpone, Hibernate, Timeout, NextEvents) ->
+  Parent, Debug,
+  #{state := State, state_enter := StateEnter} = S, StateTimer,
+  Events, Event, NextState, NewData, Actions) ->
+    case parse_actions(Debug, S, State, Actions) of
+	{ok,NewDebug,Hibernate,Timeout,StateTimeout,Postpone,NextEvents} ->
+	    if
+		StateEnter, NextState =/= State ->
+		    loop_event_enter(
+		      Parent, NewDebug, S, StateTimer,
+		      Events, Event, NextState, NewData,
+		      Hibernate, Timeout, StateTimeout, Postpone, NextEvents);
+		StateEnter ->
+		    case maps:is_key(init_state, S) of
+			true ->
+			    %% Avoid infinite loop in initial state
+			    %% with state entry events
+			    NewS = maps:remove(init_state, S),
+			    loop_event_enter(
+			      Parent, NewDebug, NewS, StateTimer,
+			      Events, Event, NextState, NewData,
+			      Hibernate, Timeout, StateTimeout,
+			      Postpone, NextEvents);
+			false ->
+			    loop_event_result(
+			      Parent, NewDebug, S, StateTimer,
+			      Events, Event, NextState, NewData,
+			      Hibernate, Timeout, StateTimeout,
+			      Postpone, NextEvents)
+		    end;
+		true ->
+		    loop_event_result(
+		      Parent, NewDebug, S, StateTimer,
+		      Events, Event, NextState, NewData,
+		      Hibernate, Timeout, StateTimeout, Postpone, NextEvents)
+	    end;
+	{Class,Reason,Stacktrace} ->
+	    terminate(
+	      Class, Reason, Stacktrace,
+	      Debug, S#{data := NewData}, [Event|Events])
+    end.
+
+loop_event_enter(
+  Parent, Debug, #{state := State} = S, StateTimer,
+  Events, Event, NextState, NewData,
+  Hibernate, Timeout, StateTimeout, Postpone, NextEvents) ->
+    case call_state_function(S, enter, State, NextState, NewData) of
+	{ok,Result,NewS} ->
+	    {NewerData,_,Actions} =
+		parse_event_result(
+		  false, Debug, NewS, Result,
+		  Events, Event, NextState, NewData),
+	    loop_event_enter_actions(
+	      Parent, Debug, NewS, StateTimer,
+	      Events, Event, NextState, NewerData,
+	      Hibernate, Timeout, StateTimeout, Postpone, NextEvents, Actions);
+	{Class,Reason,Stacktrace} ->
+	    terminate(
+	      Class, Reason, Stacktrace,
+	      Debug, S#{state := NextState, data := NewData},
+	      [Event|Events])
+    end.
+
+loop_event_enter_actions(
+  Parent, Debug, S, StateTimer,
+  Events, Event, NextState, NewData,
+  Hibernate, Timeout, StateTimeout, Postpone, NextEvents, Actions) ->
+    case
+	parse_enter_actions(
+	  Debug, S, NextState, Actions,
+	  Hibernate, Timeout, StateTimeout)
+    of
+	{ok,NewDebug,NewHibernate,NewTimeout,NewStateTimeout,_,_} ->
+	    loop_event_result(
+	      Parent, NewDebug, S, StateTimer,
+	      Events, Event, NextState, NewData,
+	      NewHibernate, NewTimeout, NewStateTimeout, Postpone, NextEvents);
+	{Class,Reason,Stacktrace} ->
+	    terminate(
+	      Class, Reason, Stacktrace,
+	      Debug, S#{state := NextState, data := NewData},
+	      [Event|Events])
+    end.
+
+loop_event_result(
+  Parent, Debug,
+  #{state := State, postponed := P_0} = S, StateTimer,
+  Events, Event, NextState, NewData,
+  Hibernate, Timeout, StateTimeout, Postpone, NextEvents) ->
     %%
     %% All options have been collected and next_events are buffered.
     %% Do the actual state transition.
     %%
-    P1 = % Move current event to postponed if Postpone
+    NewStateTimeout =
+	case StateTimeout of
+	    {state_timeout,Time,_} ->
+		%% New timeout -> cancel timer
+		case StateTimer of
+		    {state_timeout,_,_} ->
+			ok;
+		    _ ->
+			cancel_timer(StateTimer)
+		end,
+		case Time of
+		    infinity ->
+			undefined;
+		    _ ->
+			StateTimeout
+		end;
+	    undefined when NextState =/= State ->
+		%% State change -> cancel timer
+		case StateTimer of
+		    {state_timeout,_,_} ->
+			ok;
+		    _ ->
+			cancel_timer(StateTimer)
+		end,
+		undefined;
+	    undefined ->
+		StateTimer
+	end,
+    %%
+    P_1 = % Move current event to postponed if Postpone
 	case Postpone of
 	    true ->
-		[Event|P0];
+		[Event|P_0];
 	    false ->
-		P0
+		P_0
 	end,
-    {Q2,P} = % Move all postponed events to queue if state change
+    {Events_1,NewP} = % Move all postponed events to queue if state change
 	if
 	    NextState =:= State ->
-		{Events,P1};
+		{Events,P_1};
 	    true ->
-		{lists:reverse(P1, Events),[]}
+		{lists:reverse(P_1, Events),[]}
 	end,
     %% Place next events first in queue
-    Q = lists:reverse(NextEvents, Q2),
+    NewEvents = lists:reverse(NextEvents, Events_1),
     %%
     NewDebug =
 	sys_debug(
 	  Debug, S, State,
 	  case Postpone of
 	      true ->
-		  {postpone,Event,NextState};
+		  {postpone,Event,State};
 	      false ->
-		  {consume,Event,NextState}
+		  {consume,Event,State}
 	  end),
+    %%
     loop_events(
-      Parent, NewDebug, S, Q, NextState, NewData, P, Hibernate, Timeout).
+      Parent, NewDebug, S, NewStateTimeout,
+      NewEvents, Timeout, NextState, NewData, NewP, Hibernate).
 
 %%---------------------------------------------------------------------------
 %% Server helpers
 
 reply_then_terminate(
   Class, Reason, Stacktrace,
-  Debug, S, Q, State, Data, P, Replies) ->
+  Debug, #{state := State} = S, Q, Replies) ->
     if
 	is_list(Replies) ->
 	    do_reply_then_terminate(
 	      Class, Reason, Stacktrace,
-	      Debug, S, Q, State, Data, P, Replies);
+	      Debug, S, Q, Replies, State);
 	true ->
 	    do_reply_then_terminate(
 	      Class, Reason, Stacktrace,
-	      Debug, S, Q, State, Data, P, [Replies])
+	      Debug, S, Q, [Replies], State)
     end.
 %%
 do_reply_then_terminate(
-  Class, Reason, Stacktrace, Debug, S, Q, State, Data, P, []) ->
-    terminate(Class, Reason, Stacktrace, Debug, S, Q, State, Data, P);
+  Class, Reason, Stacktrace, Debug, S, Q, [], _State) ->
+    terminate(Class, Reason, Stacktrace, Debug, S, Q);
 do_reply_then_terminate(
-  Class, Reason, Stacktrace, Debug, S, Q, State, Data, P, [R|Rs]) ->
+  Class, Reason, Stacktrace, Debug, S, Q, [R|Rs], State) ->
     case R of
 	{reply,{_To,_Tag}=From,Reply} ->
 	    NewDebug = do_reply(Debug, S, State, From, Reply),
 	    do_reply_then_terminate(
-	      Class, Reason, Stacktrace,
-	      NewDebug, S, Q, State, Data, P, Rs);
+	      Class, Reason, Stacktrace, NewDebug, S, Q, Rs, State);
 	_ ->
 	    terminate(
 	      error,
 	      {bad_reply_action_from_state_function,R},
 	      ?STACKTRACE(),
-	      Debug, S, Q, State, Data, P)
+	      Debug, S, Q)
     end.
 
 do_reply(Debug, S, State, From, Reply) ->
@@ -1227,7 +1459,9 @@ do_reply(Debug, S, State, From, Reply) ->
 
 terminate(
   Class, Reason, Stacktrace,
-  Debug, #{module := Module} = S, Q, State, Data, P) ->
+  Debug,
+  #{module := Module, state := State, data := Data, postponed := P} = S,
+  Q) ->
     try Module:terminate(Reason, State, Data) of
 	_ -> ok
     catch
@@ -1236,7 +1470,7 @@ terminate(
 	    ST = erlang:get_stacktrace(),
 	    error_info(
 	      C, R, ST, S, Q, P,
-	      format_status(terminate, get(), S, State, Data)),
+	      format_status(terminate, get(), S)),
 	    sys:print_log(Debug),
 	    erlang:raise(C, R, ST)
     end,
@@ -1247,7 +1481,7 @@ terminate(
 	_ ->
 	    error_info(
 	      Class, Reason, Stacktrace, S, Q, P,
-	      format_status(terminate, get(), S, State, Data)),
+	      format_status(terminate, get(), S)),
 	    sys:print_log(Debug)
     end,
     case Stacktrace of
@@ -1259,7 +1493,9 @@ terminate(
 
 error_info(
   Class, Reason, Stacktrace,
-  #{name := Name, callback_mode := CallbackMode},
+  #{name := Name,
+    callback_mode := CallbackMode,
+    state_enter := StateEnter},
   Q, P, FmtData) ->
     {FixedReason,FixedStacktrace} =
 	case Stacktrace of
@@ -1286,6 +1522,13 @@ error_info(
 		end;
 	    _ -> {Reason,Stacktrace}
 	end,
+    CBMode =
+	 case StateEnter of
+	     true ->
+		 [CallbackMode,state_enter];
+	     false ->
+		 CallbackMode
+	 end,
     error_logger:format(
       "** State machine ~p terminating~n" ++
 	  case Q of
@@ -1312,8 +1555,9 @@ error_info(
 	   [] -> [];
 	   [Event|_] -> [Event]
        end] ++
-	  [FmtData,Class,FixedReason,
-	   CallbackMode] ++
+	  [FmtData,
+	   Class,FixedReason,
+	   CBMode] ++
 	  case Q of
 	      [_|[_|_] = Events] -> [Events];
 	      _ -> []
@@ -1329,7 +1573,9 @@ error_info(
 
 
 %% Call Module:format_status/2 or return a default value
-format_status(Opt, PDict, #{module := Module}, State, Data) ->
+format_status(
+  Opt, PDict,
+  #{module := Module, state := State, data := Data}) ->
     case erlang:function_exported(Module, format_status, 2) of
 	true ->
 	    try Module:format_status(Opt, [PDict,State,Data])
@@ -1353,3 +1599,24 @@ format_status_default(Opt, State, Data) ->
 	_ ->
 	    [{data,[{"State",StateData}]}]
     end.
+
+listify(Item) when is_list(Item) ->
+    Item;
+listify(Item) ->
+    [Item].
+
+cancel_timer(undefined) ->
+    ok;
+cancel_timer(TRef) ->
+    case erlang:cancel_timer(TRef) of
+	false ->
+	    %% We have to assume that TRef is the ref of a running timer
+	    %% and if so the timer has expired
+	    %% hence we must wait for the timeout message
+	    receive
+		{timeout,TRef,_} ->
+		    ok
+	    end;
+	_TimeLeft ->
+	    ok
+    end.
diff --git a/lib/stdlib/test/gen_statem_SUITE.erl b/lib/stdlib/test/gen_statem_SUITE.erl
index 1d1417c2e6..28f9ab81fe 100644
--- a/lib/stdlib/test/gen_statem_SUITE.erl
+++ b/lib/stdlib/test/gen_statem_SUITE.erl
@@ -37,7 +37,8 @@ all() ->
      {group, stop_handle_event},
      {group, abnormal},
      {group, abnormal_handle_event},
-     shutdown, stop_and_reply, event_order, code_change,
+     shutdown, stop_and_reply, state_enter, event_order,
+     state_timeout, code_change,
      {group, sys},
      hibernate, enter_loop].
 
@@ -57,7 +58,7 @@ tcs(start) ->
 tcs(stop) ->
     [stop1, stop2, stop3, stop4, stop5, stop6, stop7, stop8, stop9, stop10];
 tcs(abnormal) ->
-    [abnormal1, abnormal2];
+    [abnormal1, abnormal1clean, abnormal1dirty, abnormal2];
 tcs(sys) ->
     [sys1, call_format_status,
      error_format_status, terminate_crash_format,
@@ -451,8 +452,52 @@ abnormal1(Config) ->
 	   gen_statem:call(Name, {delayed_answer,1000}, 10),
 	   Reason),
     ok = gen_statem:stop(Name),
+    ?t:sleep(1100),
     ok = verify_empty_msgq().
 
+%% Check that time outs in calls work
+abnormal1clean(Config) ->
+    Name = abnormal1clean,
+    LocalSTM = {local,Name},
+
+    {ok, _Pid} =
+	gen_statem:start(LocalSTM, ?MODULE, start_arg(Config, []), []),
+
+    %% timeout call.
+    delayed =
+	gen_statem:call(Name, {delayed_answer,1}, {clean_timeout,100}),
+    {timeout,_} =
+	?EXPECT_FAILURE(
+	   gen_statem:call(
+	     Name, {delayed_answer,1000}, {clean_timeout,10}),
+	   Reason),
+    ok = gen_statem:stop(Name),
+    ?t:sleep(1100),
+    ok = verify_empty_msgq().
+
+%% Check that time outs in calls work
+abnormal1dirty(Config) ->
+    Name = abnormal1dirty,
+    LocalSTM = {local,Name},
+
+    {ok, _Pid} =
+	gen_statem:start(LocalSTM, ?MODULE, start_arg(Config, []), []),
+
+    %% timeout call.
+    delayed =
+	gen_statem:call(Name, {delayed_answer,1}, {dirty_timeout,100}),
+    {timeout,_} =
+	?EXPECT_FAILURE(
+	   gen_statem:call(
+	     Name, {delayed_answer,1000}, {dirty_timeout,10}),
+	   Reason),
+    ok = gen_statem:stop(Name),
+    ?t:sleep(1100),
+    case flush() of
+	[{Ref,delayed}] when is_reference(Ref) ->
+	    ok
+    end.
+
 %% Check that bad return values makes the stm crash. Note that we must
 %% trap exit since we must link to get the real bad_return_ error
 abnormal2(Config) ->
@@ -512,7 +557,8 @@ stop_and_reply(_Config) ->
 		      {stop_and_reply,Reason,
 		       [R1,{reply,From2,Reply2}]}
 	      end},
-    {ok,STM} = gen_statem:start_link(?MODULE, {map_statem,Machine}, []),
+    {ok,STM} =
+	gen_statem:start_link(?MODULE, {map_statem,Machine,[]}, []),
 
     Self = self(),
     Tag1 = make_ref(),
@@ -537,6 +583,61 @@ stop_and_reply(_Config) ->
 
 
 
+state_enter(_Config) ->
+    process_flag(trap_exit, true),
+    Self = self(),
+
+    Machine =
+	%% Abusing the internal format of From...
+	#{init =>
+	      fun () ->
+		      {ok,start,1}
+	      end,
+	  start =>
+	      fun (enter, Prev, N) ->
+		      Self ! {enter,start,Prev,N},
+		      {keep_state,N + 1};
+		  (internal, Prev, N) ->
+		      Self ! {internal,start,Prev,N},
+		      {keep_state,N + 1};
+		  ({call,From}, echo, N) ->
+		      {next_state,wait,N + 1,{reply,From,{echo,start,N}}};
+		  ({call,From}, {stop,Reason}, N) ->
+		      {stop_and_reply,Reason,[{reply,From,{stop,N}}],N + 1}
+	      end,
+	  wait =>
+	      fun (enter, Prev, N) ->
+		      Self ! {enter,wait,Prev,N},
+		      {keep_state,N + 1};
+		  ({call,From}, echo, N) ->
+		      {next_state,start,N + 1,
+		       [{next_event,internal,wait},
+			{reply,From,{echo,wait,N}}]}
+	      end},
+    {ok,STM} =
+	gen_statem:start_link(
+	  ?MODULE, {map_statem,Machine,[state_enter]}, []),
+
+    [{enter,start,start,1}] = flush(),
+    {echo,start,2} = gen_statem:call(STM, echo),
+    [{enter,wait,start,3}] = flush(),
+    {wait,[4|_]} = sys:get_state(STM),
+    {echo,wait,4} = gen_statem:call(STM, echo),
+    [{enter,start,wait,5},{internal,start,wait,6}] = flush(),
+    {stop,7} = gen_statem:call(STM, {stop,bye}),
+    [{'EXIT',STM,bye}] = flush(),
+
+    {noproc,_} =
+	?EXPECT_FAILURE(gen_statem:call(STM, hej), Reason),
+    case flush() of
+	[] ->
+	    ok;
+	Other2 ->
+	    ct:fail({unexpected,Other2})
+    end.
+
+
+
 event_order(_Config) ->
     process_flag(trap_exit, true),
 
@@ -579,7 +680,7 @@ event_order(_Config) ->
 		      Result
 	      end},
 
-    {ok,STM} = gen_statem:start_link(?MODULE, {map_statem,Machine}, []),
+    {ok,STM} = gen_statem:start_link(?MODULE, {map_statem,Machine,[]}, []),
     Self = self(),
     Tag1 = make_ref(),
     gen_statem:cast(STM, {reply,{Self,Tag1},ok1}),
@@ -609,6 +710,83 @@ event_order(_Config) ->
 
 
 
+state_timeout(_Config) ->
+    process_flag(trap_exit, true),
+
+    Machine =
+	#{init =>
+	      fun () ->
+		      {ok,start,0}
+	      end,
+	  start =>
+	      fun
+		  ({call,From}, {go,Time}, 0)  ->
+		      self() ! message_to_self,
+		      {next_state, state1, {Time,From},
+		       %% Verify that internal events goes before external
+		       [{state_timeout,Time,1},
+			{next_event,internal,1}]}
+	      end,
+	  state1 =>
+	      fun
+		  (internal, 1, Data) ->
+		      %% Verify that a state change cancels timeout 1
+		      {next_state, state2, Data,
+		       [{timeout,0,2},
+			{state_timeout,0,2},
+			{next_event,internal,2}]}
+	      end,
+	  state2 =>
+	      fun
+		  (internal, 2, Data) ->
+		      %% Verify that {state_timeout,0,_}
+		      %% comes after next_event and that
+		      %% {timeout,0,_} is cancelled by
+		      %% {state_timeout,0,_}
+		      {keep_state, {ok,2,Data},
+		       [{timeout,0,3}]};
+		  (state_timeout, 2, {ok,2,{Time,From}}) ->
+		      {next_state, state3, 3,
+		       [{reply,From,ok},
+			{state_timeout,Time,3}]}
+	      end,
+	  state3 =>
+	      fun
+		  (info, message_to_self, 3) ->
+		      {keep_state, '3'};
+		  ({call,From}, check, '3') ->
+		      {keep_state, From};
+		  (state_timeout, 3, From) ->
+		      {stop_and_reply, normal,
+		       {reply,From,ok}}
+	      end},
+
+    {ok,STM} = gen_statem:start_link(?MODULE, {map_statem,Machine,[]}, []),
+    TRef = erlang:start_timer(1000, self(), kull),
+    ok = gen_statem:call(STM, {go,500}),
+    ok = gen_statem:call(STM, check),
+    receive
+	{timeout,TRef,kull} ->
+	    ct:fail(late_timeout)
+    after 0 ->
+	    receive
+		{timeout,TRef,kull} ->
+		    ok
+	    after 1000 ->
+		    ct:fail(no_check_timeout)
+	    end
+    end,
+    receive
+	{'EXIT',STM,normal} ->
+	    ok
+    after 500 ->
+	    ct:fail(did_not_stop)
+    end,
+
+    verify_empty_msgq().
+
+
+
 sys1(Config) ->
     {ok,Pid} = gen_statem:start(?MODULE, start_arg(Config, []), []),
     {status, Pid, {module,gen_statem}, _} = sys:get_status(Pid),
@@ -1271,9 +1449,9 @@ init({callback_mode,CallbackMode,Arg}) ->
     ets:new(?MODULE, [named_table,private]),
     ets:insert(?MODULE, {callback_mode,CallbackMode}),
     init(Arg);
-init({map_statem,#{init := Init}=Machine}) ->
+init({map_statem,#{init := Init}=Machine,Modes}) ->
     ets:new(?MODULE, [named_table,private]),
-    ets:insert(?MODULE, {callback_mode,handle_event_function}),
+    ets:insert(?MODULE, {callback_mode,[handle_event_function|Modes]}),
     case Init() of
 	{ok,State,Data,Ops} ->
 	    {ok,State,[Data|Machine],Ops};
diff --git a/lib/tools/emacs/erlang-skels.el b/lib/tools/emacs/erlang-skels.el
index 0284c9d686..eeba7f34e9 100644
--- a/lib/tools/emacs/erlang-skels.el
+++ b/lib/tools/emacs/erlang-skels.el
@@ -904,7 +904,7 @@ Please see the function `tempo-define-template'.")
     "%% @doc" n
     "%% Define the callback_mode() for this callback module." n
     (erlang-skel-separator-end 2)
-    "-spec callback_mode() -> gen_statem:callback_mode()." n
+    "-spec callback_mode() -> gen_statem:callback_mode_result()." n
     "callback_mode() -> state_functions." n
     n
     (erlang-skel-separator-start 2)
@@ -931,14 +931,16 @@ Please see the function `tempo-define-template'.")
     "%% Whenever a gen_statem receives an event, the function " n
     "%% with the name of the current state (StateName) " n
     "%% is called to handle the event." n
-    "%%" n
-    "%% NOTE: If there is an exported function handle_event/4, it is called" n
-    "%%       instead of StateName/3 functions like this!" n
     (erlang-skel-separator-end 2)
-    "-spec state_name(" n>
-    "gen_statem:event_type(), Msg :: term()," n>
+    "-spec state_name('enter'," n>
+    "OldState :: atom()," n>
+    "Data :: term()) ->" n>
+    "gen_statem:state_enter_result('state_name');" n>
+    "(gen_statem:event_type()," n>
+    "Msg :: term()," n>
     "Data :: term()) ->" n>
-    "gen_statem:state_function_result()." n
+    "gen_statem:event_handler_result(atom())." n
+    ;;
     "state_name({call,Caller}, _Msg, Data) ->" n>
     "{next_state, state_name, Data, [{reply,Caller,ok}]}." n
     n
@@ -1015,7 +1017,7 @@ Please see the function `tempo-define-template'.")
     "%% @doc" n
     "%% Define the callback_mode() for this callback module." n
     (erlang-skel-separator-end 2)
-    "-spec callback_mode() -> gen_statem:callback_mode()." n
+    "-spec callback_mode() -> gen_statem:callback_mode_result()." n
     "callback_mode() -> handle_event_function." n
     n
     (erlang-skel-separator-start 2)
@@ -1039,14 +1041,18 @@ Please see the function `tempo-define-template'.")
     "%% @private" n
     "%% @doc" n
     "%% This function is called for every event a gen_statem receives." n
-    "%%" n
-    "%% NOTE: If there is no exported function handle_event/4," n
-    "%%       StateName/3 functions are called instead!" n
     (erlang-skel-separator-end 2)
-    "-spec handle_event(" n>
-    "gen_statem:event_type(), Msg :: term()," n>
-    "State :: term(), Data :: term()) ->" n>
-    "gen_statem:handle_event_result()." n
+    "-spec handle_event('enter'," n>
+    "OldState :: term()," n>
+    "State :: term()," n>
+    "Data :: term()) ->" n>
+    "gen_statem:state_enter_result(term());" n>
+    "(gen_statem:event_type()," n>
+    "Msg :: term()," n>
+    "State :: term()," n>
+    "Data :: term()) ->" n>
+    "gen_statem:event_handler_result(term())." n
+    ;;
     "handle_event({call,From}, _Msg, State, Data) ->" n>
     "{next_state, State, Data, [{reply,From,ok}]}." n
     n
diff --git a/system/doc/design_principles/code_lock.dia b/system/doc/design_principles/code_lock.dia
index 8e6ff8a898..eaa2aca5b0 100644
--- a/system/doc/design_principles/code_lock.dia
+++ b/system/doc/design_principles/code_lock.dia
diff --git a/system/doc/design_principles/code_lock.png b/system/doc/design_principles/code_lock.png
index 745fd91920..40bd35fc74 100644
--- a/system/doc/design_principles/code_lock.png
+++ b/system/doc/design_principles/code_lock.png
diff --git a/system/doc/design_principles/code_lock_2.dia b/system/doc/design_principles/code_lock_2.dia
index 142909a2f5..3b9ba554d8 100644
--- a/system/doc/design_principles/code_lock_2.dia
+++ b/system/doc/design_principles/code_lock_2.dia
diff --git a/system/doc/design_principles/code_lock_2.png b/system/doc/design_principles/code_lock_2.png
index ecf7b0d799..3aca9dd5aa 100644
--- a/system/doc/design_principles/code_lock_2.png
+++ b/system/doc/design_principles/code_lock_2.png
diff --git a/system/doc/design_principles/statem.xml b/system/doc/design_principles/statem.xml
index 57e47431b8..bece95e6b8 100644
--- a/system/doc/design_principles/statem.xml
+++ b/system/doc/design_principles/statem.xml
@@ -29,7 +29,7 @@
     <rev></rev>
     <file>statem.xml</file>
   </header>
-  <marker id="gen_statem behaviour"></marker>
+  <marker id="gen_statem Behaviour" />
   <p>
     This section is to be read with the
     <seealso marker="stdlib:gen_statem"><c>gen_statem(3)</c></seealso>
@@ -50,6 +50,7 @@
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Event-Driven State Machines" />
     <title>Event-Driven State Machines</title>
     <p>
       Established Automata Theory does not deal much with
@@ -94,7 +95,7 @@ State(S) x Event(E) -> Actions(A), State(S')</pre>
 <!-- =================================================================== -->
 
   <section>
-    <marker id="callback_modes" />
+    <marker id="Callback Modes" />
     <title>Callback Modes</title>
     <p>
       The <c>gen_statem</c> behavior supports two callback modes:
@@ -109,8 +110,13 @@ State(S) x Event(E) -> Actions(A), State(S')</pre>
         </p>
         <pre>
 StateName(EventType, EventContent, Data) ->
-    .. code for actions here ...
-    {next_state, NewStateName, NewData}.</pre>
+    ... code for actions here ...
+    {next_state, NewStateName, NewData}.
+	</pre>
+	<p>
+	  This form is used in most examples here for example in section
+	  <seealso marker="#Example">Example</seealso>.
+	</p>
       </item>
       <item>
         <p>
@@ -120,8 +126,14 @@ StateName(EventType, EventContent, Data) ->
         </p>
         <pre>
 handle_event(EventType, EventContent, State, Data) ->
-    .. code for actions here ...
-    {next_state, NewState, NewData}</pre>
+    ... code for actions here ...
+    {next_state, NewState, NewData}
+	</pre>
+	<p>
+	  Se section
+	  <seealso marker="#One Event Handler">One Event Handler</seealso>
+	  for an example.
+	</p>
       </item>
     </list>
     <p>
@@ -134,10 +146,11 @@ handle_event(EventType, EventContent, State, Data) ->
     </p>
 
     <section>
+      <marker id="Choosing the Callback Mode" />
       <title>Choosing the Callback Mode</title>
       <p>
 	The two
-	<seealso marker="#callback_modes">callback modes</seealso>
+	<seealso marker="#Callback Modes">callback modes</seealso>
 	give different possibilities
 	and restrictions, but one goal remains:
 	you want to handle all possible combinations of
@@ -195,10 +208,195 @@ handle_event(EventType, EventContent, State, Data) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="State Enter Calls" />
+    <title>State Enter Calls</title>
+    <p>
+      The <c>gen_statem</c> behavior can regardless of callback mode
+      automatically
+      <seealso marker="stdlib:gen_statem#type-state_enter">
+	call the state callback
+      </seealso>
+      with special arguments whenever the state changes
+      so you can write state entry actions
+      near the rest of the state transition rules.
+      It typically looks like this:
+    </p>
+    <pre>
+StateName(enter, _OldState, Data) ->
+    ... code for state entry actions here ...
+    {keep_state, NewData};
+StateName(EventType, EventContent, Data) ->
+    ... code for actions here ...
+    {next_state, NewStateName, NewData}.</pre>
+    <p>
+      Depending on how your state machine is specified,
+      this can be a very useful feature,
+      but it forces you to handle the state enter calls in all states.
+      See also the
+      <seealso marker="#State Entry Actions">
+	State Entry Actions
+      </seealso>
+      chapter.
+    </p>
+  </section>
+
+<!-- =================================================================== -->
+
+  <section>
+    <marker id="Actions" />
+    <title>Actions</title>
+    <p>
+      In the first section
+      <seealso marker="#Event-Driven State Machines">
+	Event-Driven State Machines
+      </seealso>
+      actions were mentioned as a part of
+      the general state machine model. These general actions
+      are implemented with the code that callback module
+      <c>gen_statem</c> executes in an event-handling
+      callback function before returning
+      to the <c>gen_statem</c> engine.
+    </p>
+    <p>
+      There are more specific state-transition actions
+      that a callback function can order the <c>gen_statem</c>
+      engine to do after the callback function return.
+      These are ordered by returning a list of
+      <seealso marker="stdlib:gen_statem#type-action">actions</seealso>
+      in the
+      <seealso marker="stdlib:gen_statem#type-state_callback_result">return tuple</seealso>
+      from the
+      <seealso marker="stdlib:gen_statem#Module:StateName/3">callback function</seealso>.
+      These state transition actions affect the <c>gen_statem</c>
+      engine itself and can do the following:
+    </p>
+    <list type="bulleted">
+      <item>
+	<seealso marker="stdlib:gen_statem#type-postpone">
+	  Postpone
+	</seealso>
+	the current event, see section
+	<seealso marker="#Postponing Events">Postponing Events</seealso>
+      </item>
+      <item>
+	<seealso marker="stdlib:gen_statem#type-hibernate">
+	  Hibernate
+	</seealso>
+	the <c>gen_statem</c>, treated in
+	<seealso marker="#Hibernation">Hibernation</seealso>
+      </item>
+      <item>
+	Start a
+	<seealso marker="stdlib:gen_statem#type-state_timeout">
+	  state time-out</seealso>,
+	  read more in section
+	<seealso marker="#State Time-Outs">State Time-Outs</seealso>
+      </item>
+      <item>
+	Start an
+	<seealso marker="stdlib:gen_statem#type-event_timeout">event time-out</seealso>,
+	see more in section
+	<seealso marker="#Event Time-Outs">Event Time-Outs</seealso>
+      </item>
+      <item>
+	<seealso marker="stdlib:gen_statem#type-reply_action">
+	  Reply
+	</seealso>
+	to a caller, mentioned at the end of section
+	<seealso marker="#All State Events">All State Events</seealso>
+      </item>
+      <item>
+	Generate the
+	<seealso marker="stdlib:gen_statem#type-action">
+	  next event
+	</seealso>
+	to handle, see section 
+	<seealso marker="#Self-Generated Events">Self-Generated Events</seealso>
+      </item>
+    </list>
+    <p>
+      For details, see the
+      <seealso marker="stdlib:gen_statem#type-action">
+	<c>gen_statem(3)</c>
+      </seealso>
+      manual page.
+      You can, for example, reply to many callers
+      and generate multiple next events to handle.
+    </p>
+  </section>
+
+<!-- =================================================================== -->
+
+  <section>
+    <marker id="Event Types" />
+    <title>Event Types</title>
+    <p>
+      Events are categorized in different
+      <seealso marker="stdlib:gen_statem#type-event_type">event types</seealso>.
+      Events of all types are handled in the same callback function,
+      for a given state, and the function gets
+      <c>EventType</c> and <c>EventContent</c> as arguments.
+    </p>
+    <p>
+      The following is a complete list of event types and where
+      they come from:
+    </p>
+    <taglist>
+      <tag><c>cast</c></tag>
+      <item>
+	Generated by
+	<seealso marker="stdlib:gen_statem#cast/2"><c>gen_statem:cast</c></seealso>.
+      </item>
+      <tag><c>{call,From}</c></tag>
+      <item>
+	Generated by
+	<seealso marker="stdlib:gen_statem#call/2"><c>gen_statem:call</c></seealso>,
+	where <c>From</c> is the reply address to use
+	when replying either through the state transition action
+	<c>{reply,From,Msg}</c> or by calling
+	<seealso marker="stdlib:gen_statem#reply/1"><c>gen_statem:reply</c></seealso>.
+      </item>
+      <tag><c>info</c></tag>
+      <item>
+	Generated by any regular process message sent to
+	the <c>gen_statem</c> process.
+      </item>
+      <tag><c>state_timeout</c></tag>
+      <item>
+	Generated by state transition action
+	<seealso marker="stdlib:gen_statem#type-state_timeout">
+	  <c>{state_timeout,Time,EventContent}</c>
+	</seealso>
+	state timer timing out.
+      </item>
+      <tag><c>timeout</c></tag>
+      <item>
+	Generated by state transition action
+	<seealso marker="stdlib:gen_statem#type-event_timeout">
+	  <c>{timeout,Time,EventContent}</c>
+	</seealso>
+	(or its short form <c>Time</c>)
+	event timer timing out.
+      </item>
+      <tag><c>internal</c></tag>
+      <item>
+	Generated by state transition
+	<seealso marker="stdlib:gen_statem#type-action">action</seealso>
+	<c>{next_event,internal,EventContent}</c>.
+	All event types above can also be generated using
+	<c>{next_event,EventType,EventContent}</c>.
+      </item>
+    </taglist>
+  </section>
+
+<!-- =================================================================== -->
+
+  <section>
+    <marker id="Example" />
     <title>Example</title>
     <p>
       This example starts off as equivalent to the example in section
-      <seealso marker="fsm"><c>gen_fsm</c> Behavior</seealso>.
+      <seealso marker="fsm"><c>gen_fsm</c>&nbsp;Behavior</seealso>.
       In later sections, additions and tweaks are made
       using features in <c>gen_statem</c> that <c>gen_fsm</c> does not have.
       The end of this chapter provides the example again
@@ -221,7 +419,6 @@ handle_event(EventType, EventContent, State, Data) ->
       This code lock state machine can be implemented using
       <c>gen_statem</c> with the following callback module:
     </p>
-    <marker id="ex"></marker>
     <code type="erl"><![CDATA[
 -module(code_lock).
 -behaviour(gen_statem).
@@ -241,7 +438,7 @@ button(Digit) ->
 init(Code) ->
     do_lock(),
     Data = #{code => Code, remaining => Code},
-    {ok,locked,Data}.
+    {ok, locked, Data}.
 
 callback_mode() ->
     state_functions.
@@ -252,19 +449,19 @@ locked(
     case Remaining of
         [Digit] ->
 	    do_unlock(),
-            {next_state,open,Data#{remaining := Code},10000};
+            {next_state, open, Data#{remaining := Code},
+             [{state_timeout,10000,lock}];
         [Digit|Rest] -> % Incomplete
-            {next_state,locked,Data#{remaining := Rest}};
+            {next_state, locked, Data#{remaining := Rest}};
         _Wrong ->
-            {next_state,locked,Data#{remaining := Code}}
+            {next_state, locked, Data#{remaining := Code}}
     end.
 
-open(timeout, _,  Data) ->
+open(state_timeout, lock,  Data) ->
     do_lock(),
-    {next_state,locked,Data};
+    {next_state, locked, Data};
 open(cast, {button,_}, Data) ->
-    do_lock(),
-    {next_state,locked,Data}.
+    {next_state, open, Data}.
 
 do_lock() ->
     io:format("Lock~n", []).
@@ -275,7 +472,7 @@ terminate(_Reason, State, _Data) ->
     State =/= locked andalso do_lock(),
     ok.
 code_change(_Vsn, State, Data, _Extra) ->
-    {ok,State,Data}.
+    {ok, State, Data}.
     ]]></code>
     <p>The code is explained in the next sections.</p>
   </section>
@@ -283,6 +480,7 @@ code_change(_Vsn, State, Data, _Extra) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Starting gen_statem" />
     <title>Starting gen_statem</title>
     <p>
       In the example in the previous section, <c>gen_statem</c> is
@@ -345,7 +543,7 @@ start_link(Code) ->
     <p>
       If name registration succeeds, the new <c>gen_statem</c> process
       calls callback function <c>code_lock:init(Code)</c>.
-      This function is expected to return <c>{ok,State,Data}</c>,
+      This function is expected to return <c>{ok, State, Data}</c>,
       where <c>State</c> is the initial state of the <c>gen_statem</c>,
       in this case <c>locked</c>; assuming that the door is locked to begin
       with. <c>Data</c> is the internal server data of the <c>gen_statem</c>.
@@ -386,7 +584,7 @@ callback_mode() ->
       Function
       <seealso marker="stdlib:gen_statem#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>
       selects the
-      <seealso marker="#callback_modes"><c>CallbackMode</c></seealso>
+      <seealso marker="#Callback Modes"><c>CallbackMode</c></seealso>
       for the callback module, in this case
       <seealso marker="stdlib:gen_statem#type-callback_mode"><c>state_functions</c></seealso>.
       That is, each state has got its own handler function.
@@ -397,6 +595,7 @@ callback_mode() ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Handling Events" />
     <title>Handling Events</title>
     <p>The function notifying the code lock about a button event is
       implemented using
@@ -416,11 +615,13 @@ button(Digit) ->
       The event is made into a message and sent to the <c>gen_statem</c>.
       When the event is received, the <c>gen_statem</c> calls
       <c>StateName(cast, Event, Data)</c>, which is expected to
-      return a tuple <c>{next_state,NewStateName,NewData}</c>.
+      return a tuple <c>{next_state, NewStateName, NewData}</c>,
+      or <c>{next_state, NewStateName, NewData, Actions}</c>.
       <c>StateName</c> is the name of the current state and
       <c>NewStateName</c> is the name of the next state to go to.
       <c>NewData</c> is a new value for the server data of
-      the <c>gen_statem</c>.
+      the <c>gen_statem</c>, and <c>Actions</c> is a list of
+      actions on the <c>gen_statem</c> engine.
     </p>
     <code type="erl"><![CDATA[
 locked(
@@ -429,19 +630,19 @@ locked(
     case Remaining of
         [Digit] -> % Complete
 	    do_unlock(),
-            {next_state,open,Data#{remaining := Code},10000};
+            {next_state, open, Data#{remaining := Code},
+             [{state_timeout,10000,lock}]};
         [Digit|Rest] -> % Incomplete
-            {next_state,locked,Data#{remaining := Rest}};
+            {next_state, locked, Data#{remaining := Rest}};
         [_|_] -> % Wrong
-            {next_state,locked,Data#{remaining := Code}}
+            {next_state, locked, Data#{remaining := Code}}
     end.
 
-open(timeout, _, Data) ->
+open(state_timeout, lock, Data) ->
     do_lock(),
-    {next_state,locked,Data};
+    {next_state, locked, Data};
 open(cast, {button,_}, Data) ->
-    do_lock(),
-    {next_state,locked,Data}.
+    {next_state, open, Data}.
     ]]></code>
     <p>
       If the door is locked and a button is pressed, the pressed
@@ -455,38 +656,55 @@ open(cast, {button,_}, Data) ->
       restarts from the start of the code sequence.
     </p>
     <p>
-      In state <c>open</c>, any button locks the door, as
-      any event cancels the event timer, so no
-      time-out event occurs after a button event.
+      If the whole code is correct, the server changes states
+      to <c>open</c>.
+    </p>
+    <p>
+      In state <c>open</c>, a button event is ignored
+      by staying in the same state.  This can also be done
+      by returning <c>{keep_state, Data}</c> or in this case
+      since <c>Data</c> unchanged even by returning
+      <c>keep_state_and_data</c>.
     </p>
   </section>
 
   <section>
-    <title>Event Time-Outs</title>
+    <marker id="State Time-Outs" />
+    <title>State Time-Outs</title>
     <p>
       When a correct code has been given, the door is unlocked and
       the following tuple is returned from <c>locked/2</c>:
     </p>
     <code type="erl"><![CDATA[
-{next_state,open,Data#{remaining := Code},10000};
+{next_state, open, Data#{remaining := Code},
+ [{state_timeout,10000,lock}]};
     ]]></code>
     <p>
       10,000 is a time-out value in milliseconds.
       After this time (10 seconds), a time-out occurs.
-      Then, <c>StateName(timeout, 10000, Data)</c> is called.
+      Then, <c>StateName(state_timeout, lock, Data)</c> is called.
       The time-out occurs when the door has been in state <c>open</c>
       for 10 seconds. After that the door is locked again:
     </p>
     <code type="erl"><![CDATA[
-open(timeout, _,  Data) ->
+open(state_timeout, lock,  Data) ->
     do_lock(),
-    {next_state,locked,Data};
+    {next_state, locked, Data};
     ]]></code>
+    <p>
+      The timer for a state time-out is automatically cancelled
+      when the state machine changes states.  You can restart
+      a state time-out by setting it to a new time, which cancels
+      the running timer and starts a new.  This implies that
+      you can cancel a state time-out by restarting it with
+      time <c>infinity</c>.
+    </p>
   </section>
 
 <!-- =================================================================== -->
 
   <section>
+    <marker id="All State Events" />
     <title>All State Events</title>
     <p>
       Sometimes events can arrive in any state of the <c>gen_statem</c>.
@@ -519,21 +737,24 @@ open(EventType, EventContent, Data) ->
     handle_event(EventType, EventContent, Data).
 
 handle_event({call,From}, code_length, #{code := Code} = Data) ->
-    {keep_state,Data,[{reply,From,length(Code)}]}.
+    {keep_state, Data, [{reply,From,length(Code)}]}.
     ]]></code>
     <p>
       This example uses
       <seealso marker="stdlib:gen_statem#call/2"><c>gen_statem:call/2</c></seealso>,
       which waits for a reply from the server.
       The reply is sent with a <c>{reply,From,Reply}</c> tuple
-      in an action list in the <c>{keep_state,...}</c> tuple
-      that retains the current state.
+      in an action list in the <c>{keep_state, ...}</c> tuple
+      that retains the current state.  This return form is convenient
+      when you want to stay in the current state but do not know or
+      care about what it is.
     </p>
   </section>
 
 <!-- =================================================================== -->
 
   <section>
+    <marker id="One Event Handler" />
     <title>One Event Handler</title>
     <p>
       If mode <c>handle_event_function</c> is used,
@@ -557,19 +778,19 @@ handle_event(cast, {button,Digit}, State, #{code := Code} = Data) ->
 	    case maps:get(remaining, Data) of
 		[Digit] -> % Complete
 		    do_unlock(),
-		    {next_state,open,Data#{remaining := Code},10000};
+		    {next_state, open, Data#{remaining := Code},
+                     [{state_timeout,10000,lock}};
 		[Digit|Rest] -> % Incomplete
-		    {keep_state,Data#{remaining := Rest}};
+		    {keep_state, Data#{remaining := Rest}};
 		[_|_] -> % Wrong
-		    {keep_state,Data#{remaining := Code}}
+		    {keep_state, Data#{remaining := Code}}
 	    end;
 	open ->
-	    do_lock(),
-	    {next_state,locked,Data}
+            keep_state_and_data
     end;
-handle_event(timeout, _, open, Data) ->
+handle_event(state_timeout, lock, open, Data) ->
     do_lock(),
-    {next_state,locked,Data}.
+    {next_state, locked, Data}.
 
 ...
     ]]></code>
@@ -578,9 +799,11 @@ handle_event(timeout, _, open, Data) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Stopping" />
     <title>Stopping</title>
 
     <section>
+      <marker id="In a Supervision Tree" />
       <title>In a Supervision Tree</title>
       <p>
 	If the <c>gen_statem</c> is part of a supervision tree,
@@ -620,6 +843,7 @@ terminate(_Reason, State, _Data) ->
     </section>
 
     <section>
+      <marker id="Standalone gen_statem" />
       <title>Standalone gen_statem</title>
       <p>
 	If the <c>gen_statem</c> is not part of a supervision tree,
@@ -646,127 +870,77 @@ stop() ->
 <!-- =================================================================== -->
 
   <section>
-    <title>Actions</title>
+    <marker id="Event Time-Outs" />
+    <title>Event Time-Outs</title>
     <p>
-      In the first sections actions were mentioned as a part of
-      the general state machine model. These general actions
-      are implemented with the code that callback module
-      <c>gen_statem</c> executes in an event-handling
-      callback function before returning
-      to the <c>gen_statem</c> engine.
+      A timeout feature inherited from <c>gen_statem</c>'s predecessor
+      <seealso marker="stdlib:gen_fsm"><c>gen_fsm</c></seealso>,
+      is an event time-out, that is,
+      if an event arrives the timer is cancelled.
+      You get either an event or a time-out, but not both.
     </p>
     <p>
-      There are more specific state-transition actions
-      that a callback function can order the <c>gen_statem</c>
-      engine to do after the callback function return.
-      These are ordered by returning a list of
-      <seealso marker="stdlib:gen_statem#type-action">actions</seealso>
-      in the
-      <seealso marker="stdlib:gen_statem#type-state_function_result">return tuple</seealso>
-      from the
-      <seealso marker="stdlib:gen_statem#Module:StateName/3">callback function</seealso>.
-      These state transition actions affect the <c>gen_statem</c>
-      engine itself and can do the following:
+      It is ordered by the state transition action
+      <c>{timeout,Time,EventContent}</c>, or just <c>Time</c>,
+      or even just <c>Time</c> instead of an action list
+      (the latter is a form inherited from <c>gen_fsm</c>.
     </p>
-    <list type="bulleted">
-      <item>Postpone the current event</item>
-      <item>Hibernate the <c>gen_statem</c></item>
-      <item>Start an event time-out</item>
-      <item>Reply to a caller</item>
-      <item>Generate the next event to handle</item>
-    </list>
     <p>
-      In the example earlier was mentioned the event time-out
-      and replying to a caller.
-      An example of event postponing is included later in this chapter.
-      For details, see the
-      <seealso marker="stdlib:gen_statem#type-action"><c>gen_statem(3)</c></seealso>
-      manual page.
-      You can, for example, reply to many callers
-      and generate multiple next events to handle.
+      This type of time-out is useful to for example act on inactivity.
+      Let us start restart the code sequence
+      if no button is pressed for say 30 seconds:
     </p>
-  </section>
-
-<!-- =================================================================== -->
+    <code type="erl"><![CDATA[
+...
 
-  <section>
-    <title>Event Types</title>
+locked(
+  timeout, _, 
+  #{code := Code, remaining := Remaining} = Data) ->
+    {next_state, locked, Data#{remaining := Code}};
+locked(
+  cast, {button,Digit},
+  #{code := Code, remaining := Remaining} = Data) ->
+...
+        [Digit|Rest] -> % Incomplete
+            {next_state, locked, Data#{remaining := Rest}, 30000};
+...
+     ]]></code>
     <p>
-      The previous sections mentioned a few
-      <seealso marker="stdlib:gen_statem#type-event_type">event types</seealso>.
-      Events of all types are handled in the same callback function,
-      for a given state, and the function gets
-      <c>EventType</c> and <c>EventContent</c> as arguments.
+      Whenever we receive a button event we start an event timeout
+      of 30 seconds, and if we get an event type <c>timeout</c>
+      we reset the remaining code sequence.
     </p>
     <p>
-      The following is a complete list of event types and where
-      they come from:
+      An event timeout is cancelled by any other event so you either
+      get some other event or the timeout event.  It is therefore
+      not possible nor needed to cancel or restart an event timeout.
+      Whatever event you act on has already cancelled
+      the event timeout...
     </p>
-    <taglist>
-      <tag><c>cast</c></tag>
-      <item>
-	Generated by
-	<seealso marker="stdlib:gen_statem#cast/2"><c>gen_statem:cast</c></seealso>.
-      </item>
-      <tag><c>{call,From}</c></tag>
-      <item>
-	Generated by
-	<seealso marker="stdlib:gen_statem#call/2"><c>gen_statem:call</c></seealso>,
-	where <c>From</c> is the reply address to use
-	when replying either through the state transition action
-	<c>{reply,From,Msg}</c> or by calling
-	<seealso marker="stdlib:gen_statem#reply/1"><c>gen_statem:reply</c></seealso>.
-      </item>
-      <tag><c>info</c></tag>
-      <item>
-	Generated by any regular process message sent to
-	the <c>gen_statem</c> process.
-      </item>
-      <tag><c>timeout</c></tag>
-      <item>
-	Generated by state transition action
-	<c>{timeout,Time,EventContent}</c> (or its short form <c>Time</c>)
-	timer timing out.
-      </item>
-      <tag><c>internal</c></tag>
-      <item>
-	Generated by state transition action
-	<c>{next_event,internal,EventContent}</c>.
-	All event types above can also be generated using
-	<c>{next_event,EventType,EventContent}</c>.
-      </item>
-    </taglist>
   </section>
 
 <!-- =================================================================== -->
 
   <section>
-    <title>State Time-Outs</title>
+    <marker id="Erlang Timers" />
+    <title>Erlang Timers</title>
     <p>
-      The time-out event generated by state transition action
-      <c>{timeout,Time,EventContent}</c> is an event time-out,
-      that is, if an event arrives the timer is cancelled.
-      You get either an event or a time-out, but not both.
+      The previous example of state time-outs only work if
+      the state machine stays in the same state during the
+      time-out time.  And event time-outs only work if no
+      disturbing unrelated events occur.
     </p>
     <p>
-      Often you want a timer not to be cancelled by any event
-      or you want to start a timer in one state and respond
-      to the time-out in another. This can be accomplished
-      with a regular Erlang timer:
-      <seealso marker="erts:erlang#start_timer/4"><c>erlang:start_timer</c></seealso>.
+      You may want to start a timer in one state and respond
+      to the time-out in another, maybe cancel the time-out
+      without changing states, or perhaps run multiple
+      time-outs in parallel. All this can be accomplished
+      with Erlang Timers:
+      <seealso marker="erts:erlang#start_timer/4"><c>erlang:start_timer3,4</c></seealso>.
     </p>
     <p>
-      For the example so far in this chapter: using the
-      <c>gen_statem</c> event timer has the consequence that
-      if a button event is generated while in the <c>open</c> state,
-      the time-out is cancelled and the button event is delivered.
-      So, we choose to lock the door if this occurred.
-    </p>
-    <p>
-      Suppose that we do not want a button to lock the door,
-      instead we want to ignore button events in the <c>open</c> state.
-      Then we start a timer when entering the <c>open</c> state
-      and wait for it to expire while ignoring button events:
+      Here is how to accomplish the state time-out
+      in the previous example by insted using an Erlang Timer:
     </p>
     <code type="erl"><![CDATA[
 ...
@@ -777,25 +951,37 @@ locked(
         [Digit] ->
 	    do_unlock(),
 	    Tref = erlang:start_timer(10000, self(), lock),
-            {next_state,open,Data#{remaining := Code, timer := Tref}};
+            {next_state, open, Data#{remaining := Code, timer => Tref}};
 ...
 
 open(info, {timeout,Tref,lock}, #{timer := Tref} = Data) ->
     do_lock(),
-    {next_state,locked,Data};
+    {next_state,locked,maps:remove(timer, Data)};
 open(cast, {button,_}, Data) ->
     {keep_state,Data};
 ...
     ]]></code>
     <p>
+      Removing the <c>timer</c> key from the map when we
+      change to state <c>locked</c> is not strictly
+      necessary since we can only get into state <c>open</c>
+      with an updated <c>timer</c> map value.  But it can be nice
+      to not have outdated values in the state <c>Data</c>!
+    </p>
+    <p>
       If you need to cancel a timer because of some other event, you can use
       <seealso marker="erts:erlang#cancel_timer/2"><c>erlang:cancel_timer(Tref)</c></seealso>.
-      Notice that a time-out message cannot arrive after this,
-      unless you have postponed it (see the next section) before,
+      Note that a time-out message cannot arrive after this,
+      unless you have postponed it before (see the next section),
       so ensure that you do not accidentally postpone such messages.
+      Also note that a time-out message may have arrived
+      just before you cancelling it, so you may have to read out
+      such a message from the process mailbox depending on
+      the return value from 
+      <seealso marker="erts:erlang#cancel_timer/2"><c>erlang:cancel_timer(Tref)</c></seealso>.
     </p>
     <p>
-      Another way to cancel a timer is not to cancel it,
+      Another way to handle a late time-out can be to not cancel it,
       but to ignore it if it arrives in a state
       where it is known to be late.
     </p>
@@ -804,6 +990,7 @@ open(cast, {button,_}, Data) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Postponing Events" />
     <title>Postponing Events</title>
     <p>
       If you want to ignore a particular event in the current state
@@ -842,6 +1029,7 @@ open(cast, {button,_}, Data) ->
     </p>
 
     <section>
+      <marker id="Fuzzy State Diagrams" />
       <title>Fuzzy State Diagrams</title>
       <p>
 	It is not uncommon that a state diagram does not specify
@@ -858,6 +1046,7 @@ open(cast, {button,_}, Data) ->
     </section>
 
     <section>
+      <marker id="Selective Receive" />
       <title>Selective Receive</title>
       <p>
         Erlang's selective receive statement is often used to
@@ -937,6 +1126,59 @@ do_unlock() ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="State Entry Actions" />
+    <title>State Entry Actions</title>
+    <p>
+      Say you have a state machine specification
+      that uses state entry actions.
+      Allthough you can code this using self-generated events
+      (described in the next section), especially if just
+      one or a few states has got state entry actions,
+      this is a perfect use case for the built in
+      <seealso marker="#State Enter Calls">state enter calls</seealso>.
+    </p>
+    <p>
+      You return a list containing <c>state_enter</c> from your
+      <seealso marker="stdlib:gen_statem#Module:callback_mode/0"><c>callback_mode/0</c></seealso>
+      function and the <c>gen_statem</c> engine will call your
+      state callback once with the arguments
+      <c>(enter, OldState, ...)</c> whenever the state changes.
+      Then you just need to handle these event-like calls in all states.
+    </p>
+    <code type="erl"><![CDATA[
+...
+init(Code) ->
+    process_flag(trap_exit, true),
+    Data = #{code => Code},
+    {ok, locked, Data}.
+
+callback_mode() ->
+    [state_functions,state_enter].
+
+locked(enter, _OldState, Data) ->
+    do_lock(),
+    {keep_state,Data#{remaining => Code}};
+locked(
+  cast, {button,Digit},
+  #{code := Code, remaining := Remaining} = Data) ->
+    case Remaining of
+        [Digit] ->
+	    {next_state, open, Data};
+...
+
+open(enter, _OldState, _Data) ->
+    do_unlock(),
+    {keep_state_and_data, [{state_timeout,10000,lock}]};
+open(state_timeout, lock, Data) ->
+    {next_state, locked, Data};
+...
+    ]]></code>
+  </section>
+
+<!-- =================================================================== -->
+
+  <section>
+    <marker id="Self-Generated Events" />
     <title>Self-Generated Events</title>
     <p>
       It can sometimes be beneficial to be able to generate events
@@ -954,64 +1196,71 @@ do_unlock() ->
       from your state machine to itself.
     </p>
     <p>
-      One example of using self-generated events can be when you have
-      a state machine specification that uses state entry actions.
-      You can code that using a dedicated function
-      to do the state transition. But if you want that code to be
-      visible besides the other state logic, you can insert
-      an <c>internal</c> event that does the entry actions.
-      This has the same unfortunate consequence as using
-      state transition functions: everywhere you go to
-      the state, you must explicitly
-      insert the <c>internal</c> event
-      or use a state transition function.
+      One example for this is to pre-process incoming data, for example
+      decrypting chunks or collecting characters up to a line break.
+      Purists may argue that this should be modelled with a separate
+      state machine that sends pre-processed events
+      to the main state machine.
+      But to decrease overhead the small pre-processing state machine
+      can be implemented in the common state event handling
+      of the main state machine using a few state data variables
+      that then sends the pre-processed events as internal events
+      to the main state machine.
     </p>
     <p>
-      The following is an implementation of entry actions
-      using <c>internal</c> events with content <c>enter</c>
-      using a helper function <c>enter/3</c> for state entry:
+      The following example uses an input model where you give the lock
+      characters with <c>put_chars(Chars)</c> and then call
+      <c>enter()</c> to finish the input.
     </p>
     <code type="erl"><![CDATA[
 ...
-init(Code) ->
-    process_flag(trap_exit, true),
-    Data = #{code => Code},
-    enter(ok, locked, Data).
+-export(put_chars/1, enter/0).
+...
+put_chars(Chars) when is_binary(Chars) ->
+    gen_statem:call(?NAME, {chars,Chars}).
 
-callback_mode() ->
-    state_functions.
+enter() ->
+    gen_statem:call(?NAME, enter).
 
-locked(internal, enter, _Data) ->
-    do_lock(),
-    {keep_state,Data#{remaining => Code}};
-locked(
-  cast, {button,Digit},
-  #{code := Code, remaining := Remaining} = Data) ->
-    case Remaining of
-        [Digit] ->
-            enter(next_state, open, Data);
 ...
 
-open(internal, enter, _Data) ->
-    Tref = erlang:start_timer(10000, self(), lock),
-    do_unlock(),
-    {keep_state,Data#{timer => Tref}};
-open(info, {timeout,Tref,lock}, #{timer := Tref} = Data) ->
-    enter(next_state, locked, Data);
+locked(enter, _OldState, Data) ->
+    do_lock(),
+    {keep_state,Data#{remaining => Code, buf => []}};
 ...
 
-enter(Tag, State, Data) ->
-    {Tag,State,Data,[{next_event,internal,enter}]}.
+handle_event({call,From}, {chars,Chars}, #{buf := Buf} = Data) ->
+    {keep_state, Data#{buf := [Chars|Buf],
+     [{reply,From,ok}]};
+handle_event({call,From}, enter, #{buf := Buf} = Data) ->
+    Chars = unicode:characters_to_binary(lists:reverse(Buf)),
+    try binary_to_integer(Chars) of
+        Digit ->
+            {keep_state, Data#{buf := []},
+             [{reply,From,ok},
+              {next_event,internal,{button,Chars}}]}
+    catch
+        error:badarg ->
+            {keep_state, Data#{buf := []},
+             [{reply,From,{error,not_an_integer}}]}
+    end;
+...
     ]]></code>
+    <p>
+      If you start this program with <c>code_lock:start([17])</c>
+      you can unlock with <c>code_lock:put_chars(&lt;&lt;"001">>),
+      code_lock:put_chars(&lt;&lt;"7">>), code_lock:enter()</c>.
+    </p>
   </section>
 
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Example Revisited" />
     <title>Example Revisited</title>
     <p>
-      This section includes the example after all mentioned modifications
-      and some more using the entry actions,
+      This section includes the example after most of the mentioned
+      modifications and some more using state enter calls,
       which deserves a new state diagram:
     </p>
     <image file="../design_principles/code_lock_2.png">
@@ -1027,6 +1276,7 @@ enter(Tag, State, Data) ->
     </p>
 
     <section>
+      <marker id="Callback Mode: state_functions" />
       <title>Callback Mode: state_functions</title>
       <p>
 	Using state functions:
@@ -1054,43 +1304,44 @@ code_length() ->
 init(Code) ->
     process_flag(trap_exit, true),
     Data = #{code => Code},
-    enter(ok, locked, Data).
+    {ok, locked, Data}.
 
 callback_mode() ->
-    state_functions.
+    [state_functions,state_enter].
 
-locked(internal, enter, #{code := Code} = Data) ->
+locked(enter, _OldState, #{code := Code} = Data) ->
     do_lock(),
-    {keep_state,Data#{remaining => Code}};
+    {keep_state, Data#{remaining => Code}};
+locked(
+  timeout, _, 
+  #{code := Code, remaining := Remaining} = Data) ->
+    {keep_state, Data#{remaining := Code}};
 locked(
   cast, {button,Digit},
   #{code := Code, remaining := Remaining} = Data) ->
     case Remaining of
         [Digit] -> % Complete
-            enter(next_state, open, Data);
+            {next_state, open, Data};
         [Digit|Rest] -> % Incomplete
-            {keep_state,Data#{remaining := Rest}};
+            {keep_state, Data#{remaining := Rest}, 30000};
         [_|_] -> % Wrong
-            {keep_state,Data#{remaining := Code}}
+            {keep_state, Data#{remaining := Code}}
     end;
 locked(EventType, EventContent, Data) ->
     handle_event(EventType, EventContent, Data).
 
-open(internal, enter, Data) ->
-    Tref = erlang:start_timer(10000, self(), lock),
+open(enter, _OldState, _Data) ->
     do_unlock(),
-    {keep_state,Data#{timer => Tref}};
-open(info, {timeout,Tref,lock}, #{timer := Tref} = Data) ->
-    enter(next_state, locked, Data);
+    {keep_state_and_data, [{state_timeout,10000,lock}]};
+open(state_timeout, lock, Data) ->
+    {next_state, locked, Data};
 open(cast, {button,_}, _) ->
-    {keep_state_and_data,[postpone]};
+    {keep_state_and_data, [postpone]};
 open(EventType, EventContent, Data) ->
     handle_event(EventType, EventContent, Data).
 
 handle_event({call,From}, code_length, #{code := Code}) ->
-    {keep_state_and_data,[{reply,From,length(Code)}]}.
-enter(Tag, State, Data) ->
-    {Tag,State,Data,[{next_event,internal,enter}]}.
+    {keep_state_and_data, [{reply,From,length(Code)}]}.
 
 do_lock() ->
     io:format("Locked~n", []).
@@ -1106,13 +1357,14 @@ code_change(_Vsn, State, Data, _Extra) ->
     </section>
 
     <section>
+      <marker id="Callback Mode: handle_event_function" />
       <title>Callback Mode: handle_event_function</title>
       <p>
         This section describes what to change in the example
         to use one <c>handle_event/4</c> function.
         The previously used approach to first branch depending on event
-	does not work that well here because of the generated
-        entry actions, so this example first branches depending on state:
+	does not work that well here because of the state enter calls,
+        so this example first branches depending on state:
       </p>
       <code type="erl"><![CDATA[
 ...
@@ -1120,44 +1372,49 @@ code_change(_Vsn, State, Data, _Extra) ->
 
 ...
 callback_mode() ->
-    handle_event_function.
+    [handle_event_function,state_enter].
 
 %% State: locked
-handle_event(internal, enter, locked, #{code := Code} = Data) ->
+handle_event(
+  enter, _OldState, locked,
+  #{code := Code} = Data) ->
     do_lock(),
-    {keep_state,Data#{remaining => Code}};
+    {keep_state, Data#{remaining => Code}};
+handle_event(
+  timeout, _, locked,
+  #{code := Code, remaining := Remaining} = Data) ->
+    {keep_state, Data#{remaining := Code}};
 handle_event(
   cast, {button,Digit}, locked,
   #{code := Code, remaining := Remaining} = Data) ->
     case Remaining of
         [Digit] -> % Complete
-            enter(next_state, open, Data);
+            {next_state, open, Data};
         [Digit|Rest] -> % Incomplete
-            {keep_state,Data#{remaining := Rest}};
+            {keep_state, Data#{remaining := Rest}, 30000};
         [_|_] -> % Wrong
-            {keep_state,Data#{remaining := Code}}
+            {keep_state, Data#{remaining := Code}}
     end;
 %%
 %% State: open
-handle_event(internal, enter, open, Data) ->
-    Tref = erlang:start_timer(10000, self(), lock),
+handle_event(enter, _OldState, open, _Data) ->
     do_unlock(),
-    {keep_state,Data#{timer => Tref}};
-handle_event(info, {timeout,Tref,lock}, open, #{timer := Tref} = Data) ->
-    enter(next_state, locked, Data);
+    {keep_state_and_data, [{state_timeout,10000,lock}]};
+handle_event(state_timeout, lock, open, Data) ->
+    {next_state, locked, Data};
 handle_event(cast, {button,_}, open, _) ->
     {keep_state_and_data,[postpone]};
 %%
 %% Any state
 handle_event({call,From}, code_length, _State, #{code := Code}) ->
-    {keep_state_and_data,[{reply,From,length(Code)}]}.
+    {keep_state_and_data, [{reply,From,length(Code)}]}.
 
 ...
       ]]></code>
     </section>
     <p>
       Notice that postponing buttons from the <c>locked</c> state
-      to the <c>open</c> state feels like the wrong thing to do
+      to the <c>open</c> state feels like a strange thing to do
       for a code lock, but it at least illustrates event postponing.
     </p>
   </section>
@@ -1165,6 +1422,7 @@ handle_event({call,From}, code_length, _State, #{code := Code}) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Filter the State" />
     <title>Filter the State</title>
     <p>
       The example servers so far in this chapter
@@ -1225,12 +1483,13 @@ format_status(Opt, [_PDict,State,Data]) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Complex State" />
     <title>Complex State</title>
     <p>
       The callback mode
       <seealso marker="stdlib:gen_statem#type-callback_mode"><c>handle_event_function</c></seealso>
       enables using a non-atom state as described in section
-      <seealso marker="#callback_modes">Callback Modes</seealso>,
+      <seealso marker="#Callback Modes">Callback Modes</seealso>,
       for example, a complex state term like a tuple.
     </p>
     <p>
@@ -1304,71 +1563,68 @@ set_lock_button(LockButton) ->
 
 init({Code,LockButton}) ->
     process_flag(trap_exit, true),
-    Data = #{code => Code, remaining => undefined, timer => undefined},
-    enter(ok, {locked,LockButton}, Data, []).
+    Data = #{code => Code, remaining => undefined},
+    {ok, {locked,LockButton}, Data}.
 
 callback_mode() ->
-    handle_event_function.
+    [handle_event_function,state_enter].
 
 handle_event(
   {call,From}, {set_lock_button,NewLockButton},
   {StateName,OldLockButton}, Data) ->
-    {next_state,{StateName,NewLockButton},Data,
+    {next_state, {StateName,NewLockButton}, Data,
      [{reply,From,OldLockButton}]};
 handle_event(
   {call,From}, code_length,
   {_StateName,_LockButton}, #{code := Code}) ->
     {keep_state_and_data,
-     [{reply,From,length(Code)}]};
+    [{reply,From,length(Code)}]};
+%%
+%% State: locked
 handle_event(
   EventType, EventContent,
   {locked,LockButton}, #{code := Code, remaining := Remaining} = Data) ->
-    case {EventType,EventContent} of
-	{internal,enter} ->
+    case {EventType, EventContent} of
+	{enter, _OldState} ->
 	    do_lock(),
-	    {keep_state,Data#{remaining := Code}};
-	{{call,From},{button,Digit}} ->
+	    {keep_state, Data#{remaining := Code}};
+        {timeout, _} ->
+            {keep_state, Data#{remaining := Code}};
+	{{call,From}, {button,Digit}} ->
 	    case Remaining of
 		[Digit] -> % Complete
-		    next_state(
-		      {open,LockButton}, Data,
-		      [{reply,From,ok}]);
+		    {next_state, {open,LockButton}, Data,
+		     [{reply,From,ok}]};
 		[Digit|Rest] -> % Incomplete
-		    {keep_state,Data#{remaining := Rest},
+		    {keep_state, Data#{remaining := Rest, 30000},
 		     [{reply,From,ok}]};
 		[_|_] -> % Wrong
-		    {keep_state,Data#{remaining := Code},
+		    {keep_state, Data#{remaining := Code},
 		     [{reply,From,ok}]}
 	    end
     end;
+%%
+%% State: open
 handle_event(
   EventType, EventContent,
-  {open,LockButton}, #{timer := Timer} = Data) ->
-    case {EventType,EventContent} of
-	{internal,enter} ->
-	    Tref = erlang:start_timer(10000, self(), lock),
+  {open,LockButton}, Data) ->
+    case {EventType, EventContent} of
+	{enter, _OldState} ->
 	    do_unlock(),
-	    {keep_state,Data#{timer := Tref}};
-	{info,{timeout,Timer,lock}} ->
-	    next_state({locked,LockButton}, Data, []);
-	{{call,From},{button,Digit}} ->
+	    {keep_state_and_data, [{state_timeout,10000,lock}]};
+	{state_timeout, lock} ->
+	    {next_state, {locked,LockButton}, Data};
+	{{call,From}, {button,Digit}} ->
 	    if
 		Digit =:= LockButton ->
-		    erlang:cancel_timer(Timer),
-		    next_state(
-		      {locked,LockButton}, Data,
-		      [{reply,From,locked}]);
+		    {next_state, {locked,LockButton}, Data,
+		     [{reply,From,locked}]);
 		true ->
 		    {keep_state_and_data,
 		     [postpone]}
 	    end
     end.
 
-next_state(State, Data, Actions) ->
-    enter(next_state, State, Data, Actions).
-enter(Tag, State, Data, Actions) ->
-    {Tag,State,Data,[{next_event,internal,enter}|Actions]}.
-
 do_lock() ->
     io:format("Locked~n", []).
 do_unlock() ->
@@ -1405,6 +1661,7 @@ format_status(Opt, [_PDict,State,Data]) ->
 <!-- =================================================================== -->
 
   <section>
+    <marker id="Hibernation" />
     <title>Hibernation</title>
     <p>
       If you have many servers in one node
@@ -1430,20 +1687,21 @@ format_status(Opt, [_PDict,State,Data]) ->
     </p>
     <code type="erl"><![CDATA[
 ...
+%% State: open
 handle_event(
   EventType, EventContent,
-  {open,LockButton}, #{timer := Timer} = Data) ->
-    case {EventType,EventContent} of
-	{internal,enter} ->
-	    Tref = erlang:start_timer(10000, self(), lock),
+  {open,LockButton}, Data) ->
+    case {EventType, EventContent} of
+	{enter, _OldState} ->
 	    do_unlock(),
-	    {keep_state,Data#{timer := Tref},[hibernate]};
+	    {keep_state_and_data,
+	    [{state_timeout,10000,lock},hibernate]};
 ...
     ]]></code>
     <p>
-      The
-      <seealso marker="stdlib:gen_statem#type-hibernate"><c>[hibernate]</c></seealso>
-      action list on the last line
+      The atom
+      <seealso marker="stdlib:gen_statem#type-hibernate"><c>hibernate</c></seealso>
+      in the action list on the last line
       when entering the <c>{open,_}</c> state is the only change.
       If any event arrives in the <c>{open,_},</c> state, we
       do not bother to rehibernate, so the server stays
@@ -1458,6 +1716,10 @@ handle_event(
       <c>{open,_}</c> state, which would clutter the code.
     </p>
     <p>
+      Another not uncommon scenario is to use the event time-out
+      to triger hibernation after a certain time of inactivity.
+    </p>
+    <p>
       This server probably does not use
       heap memory worth hibernating for.
       To gain anything from hibernation, your server would