diff --git a/README.md b/README.md
index 7559257..54a00c3 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@ Here, we define the net to have the five places in the cookie vending machine.
 
 #### trsn_lst/0
 
-The `trsn_lst/0` function lets us define the names of all transitions in the net:
+The `trsn_lst/0` function lets us define the names of all transitions in the net.
 
     trsn_lst() ->
       [a, b].
@@ -105,9 +105,9 @@ Here, the firing of the transition `a` produces a `coin` token on the `cash_box`
 
 ### Interface Callback Functions
 
-In addition to the net callback functions there are another six callback functions that determine how the net instance appears as an Erlang actor to the outside world:
+In addition to the structure callback functions there are another six callback functions that determine how the net instance appears as an Erlang actor to the outside world:
 
-- `code_change/3` determines what happens when a hot code reload happens
+- `code_change/3` determines what happens when a hot code reload appears
 - `handle_call/3` synchronous message exchange
 - `handle_cast/2` asynchronous message reception
 - `handle_info/2` asynchronous reception of an unformatted message
@@ -116,7 +116,7 @@ In addition to the net callback functions there are another six callback functio
 
 #### code_change/3
 
-The `code_change/3` function determines what happens when a hot code reload happens. This callback is identical to the `code_change/3` function in the `gen_server` behavior.
+The `code_change/3` function determines what happens when a hot code reload appears. This callback is identical to the `code_change/3` function in the `gen_server` behavior.
 
     code_change( _OldVsn, NetState, _Extra ) -> {ok, NetState}.
 
diff --git a/src/gen_pnet.erl b/src/gen_pnet.erl
index 0b2cea6..57e2fad 100644
--- a/src/gen_pnet.erl
+++ b/src/gen_pnet.erl
@@ -2,7 +2,7 @@
 %%
 %% A generic Petri net OTP behavior.
 %%
-%% Copyright 2016 Jorgen Brandt. All Rights Reserved.
+%% Copyright 2016-2017 Jorgen Brandt.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -16,7 +16,21 @@
 %% See the License for the specific language governing permissions and
 %% limitations under the License.
 %%
+%% -------------------------------------------------------------------
 %% @author Jorgen Brandt <joergen.brandt@onlinehome.de>
+%% @version 0.1.1
+%% @copyright 2016-2017 Jorgen Brandt.
+%% @see gen_pnet_iface
+%% @see gen_pnet_struct
+%% @doc Callback function definitions and API for the `gen_pnet' behavior.
+%%
+%% The callbacks defined for the `gen_pnet' behavior may be separated into a
+%% Petri net structure part and an actor interface part. Both behaviors are
+%% documented in the `gen_pnet_struct' and `gen_pnet_iface' modules
+%% respectively.
+%%
+%% @end
+%% -------------------------------------------------------------------
 
 -module( gen_pnet ).
 
@@ -54,7 +68,7 @@
 -callback trigger( Place :: atom(), Token :: _ ) -> pass | drop.
 
 
-%% Net callbacks
+%% Structure callbacks
 
 -callback place_lst() -> [atom()].
 
diff --git a/src/gen_pnet_iface.erl b/src/gen_pnet_iface.erl
index a9f22bc..d55cd68 100644
--- a/src/gen_pnet_iface.erl
+++ b/src/gen_pnet_iface.erl
@@ -2,7 +2,7 @@
 %%
 %% A generic Petri net OTP behavior.
 %%
-%% Copyright 2016 Jorgen Brandt. All Rights Reserved.
+%% Copyright 2016-2017 Jorgen Brandt.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -16,7 +16,133 @@
 %% See the License for the specific language governing permissions and
 %% limitations under the License.
 %%
+%% -------------------------------------------------------------------
 %% @author Jorgen Brandt <joergen.brandt@onlinehome.de>
+%% @version 0.1.1
+%% @copyright 2016-2017 Jorgen Brandt.
+%% @doc Callback function definitions for Petri net actor interface.
+%%
+%% In addition to the structure callback functions there are another six
+%% callback functions that determine how the net instance appears as an Erlang
+%% actor to the outside world:
+%%
+%% <ul>
+%%   <li>`code_change/3' determines what happens when a hot code reload
+%%       appears</li>
+%%   <li>`handle_call/3' synchronous message exchange</li>
+%%   <li>`handle_cast/2' asynchronous message reception</li>
+%%   <li>`handle_info/2' asynchronous reception of an unformatted message</li>
+%%   <li>`terminate/2' determines what happens when the net instance is
+%%       stopped</li>
+%%   <li>`trigger/2' allows to add a side effects to the generation of a
+%%       token</li>
+%% </ul>
+%%
+%% <h4>code_change/3</h4>
+%%
+%% The `code_change/3' function determines what happens when a hot code reload
+%% appears. This callback is identical to the `code_change/3' function in the
+%% `gen_server' behavior.
+%%
+%% Example:
+%% ```
+%% code_change( _OldVsn, NetState, _Extra ) -> {ok, NetState}.
+%% '''
+%%
+%% <h4>handle_call/3</h4>
+%%
+%% The `handle_call/3' function performs a synchronous exchange of messages
+%% between the caller and the net instance. The first argument is the request
+%% message, the second argument is a tuple identifying the caller, and the third
+%% argument is a `#net_state{}' record instance describing the current state of
+%% the net. The `handle_call/3' function can either generate a reply without
+%% changing the net marking by returning a `{reply, Reply}' tuple or it can
+%% generate a reply, consuming or producing tokens by returning a
+%% `{reply, Reply, ConsumeMap, ProduceMap}' tuple.
+%%
+%% Example:
+%% ```
+%% handle_call( insert_coin, _, _ ) ->
+%%   {reply, ok, #{}, #{ coin_slot => [coin] }};
+%%
+%% handle_call( remove_cookie_box, _,
+%%              #net_state{ marking = #{ compartment := C } } ) ->
+%%
+%%   case C of
+%%     []    -> {reply, {error, empty_compartment}};
+%%     [_|_] -> {reply, ok, #{ compartment => [cookie_box] }, #{}}
+%%   end;
+%%
+%% handle_call( _, _, _ ) -> {reply, {error, bad_msg}}.
+%% '''
+%% Here, we react to two kinds of messages: Inserting a coin in the coin slot
+%% and removing a cookie box from the compartment. Thus, we react to an
+%% `insert_coin' message by replying with `ok', consuming nothing and producing
+%% a `coin' token on the `coin_slot' place. When receiving a `remove_cookie_box'
+%% message, we check whether the `compartment' place is empty, replying with an
+%% error message if it is, otherwise replying with `ok', consuming one
+%% `cookie_box' token from the `compartment' place, and producing nothing. Calls
+%% that are neither `insert_coin' nor `remove_cookie_box' are responded to with
+%% an error message.
+%%
+%% <h4>handle_cast/2</h4>
+%%
+%% The `handle_cast/2' function reacts to an asynchronous message received by
+%% the net instance. The first argument is the request while the second argument
+%% is a `#net_state{}' record instance. The `handle_cast/2' function can either
+%% leave the net unchanged by returning `noreply' or it can consume or produce
+%% tokens by returning a `{noreply, ConsumeMap, ProduceMap}' tuple.
+%%
+%% Example:
+%% ```
+%% handle_cast( _Request, _NetState ) -> noreply.
+%% '''
+%% Here, we just ignore any cast.
+%%
+%% <h4>handle_info/2</h4>
+%%
+%% The `handle_info/2' function reacts to an asynchronous, unformatted message
+%% received by the net instance. The first argument is the message term while
+%% the second argument is a `#net_state{}' record instance. The `handle_info/2'
+%% function can either leave the net unchanged by returning `noreply' or it can
+%% consume or produce tokens by returning a `{noreply, ConsumeMap, ProduceMap}'
+%% tuple.
+%%
+%% Example:
+%% ```
+%% handle_info( _Request, _NetState ) -> noreply.
+%% '''
+%% Here, we just ignore any message.
+%%
+%% <h4>terminate/2</h4>
+%%
+%% The `terminate/2' function determines what happens when the net instance is
+%% stopped. The first argument is the reason for termination while the second
+%% argument is a `#net_state{}' record instance. This callback is identical to
+%% the `terminate/2' function in the `gen_server' behavior.
+%%
+%% Example:
+%% ```
+%% terminate( _Reason, _NetState ) -> ok.
+%% '''
+%%
+%% <h4>trigger/2</h4>
+%%
+%% The `trigger/2' function determines what happens when a token is produced on
+%% a given place. Its first argument is the place name and its second argument
+%% is the token about to be produced. The `trigger/2' function is expected to
+%% return either `pass' in which case the token is produced normally, or `drop'
+%% in which case the token is forgotten.
+%%
+%% Example:
+%% ```
+%% trigger( _, _ ) -> pass.
+%% '''
+%% Here, we simply let any token pass.
+%%
+%% @end
+%% -------------------------------------------------------------------
+
 
 
 
diff --git a/src/gen_pnet_net.erl b/src/gen_pnet_net.erl
deleted file mode 100644
index fb01820..0000000
--- a/src/gen_pnet_net.erl
+++ /dev/null
@@ -1,34 +0,0 @@
-%% -*- erlang -*-
-%%
-%% A generic Petri net OTP behavior.
-%%
-%% Copyright 2016 Jorgen Brandt. All Rights Reserved.
-%%
-%% Licensed under the Apache License, Version 2.0 (the "License");
-%% you may not use this file except in compliance with the License.
-%% You may obtain a copy of the License at
-%%
-%%     http://www.apache.org/licenses/LICENSE-2.0
-%%
-%% Unless required by applicable law or agreed to in writing, software
-%% distributed under the License is distributed on an "AS IS" BASIS,
-%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-%% See the License for the specific language governing permissions and
-%% limitations under the License.
-%%
-%% @author Jorgen Brandt <joergen.brandt@onlinehome.de>
-
--module( gen_pnet_net ).
-
--callback place_lst() -> [atom()].
-
--callback trsn_lst() -> [atom()].
-
--callback init_marking( atom() ) -> [_].
-
--callback preset( Place :: atom() ) -> [atom()].
-
--callback is_enabled( Trsn :: atom(), Mode :: #{ atom() => [_]} ) -> boolean().
-
--callback fire( Trsn :: atom(), Mode :: #{ atom() => [_] } ) ->
-            abort | {produce, #{ atom() => [_] }}.
diff --git a/src/gen_pnet_struct.erl b/src/gen_pnet_struct.erl
new file mode 100644
index 0000000..d72899e
--- /dev/null
+++ b/src/gen_pnet_struct.erl
@@ -0,0 +1,149 @@
+%% -*- erlang -*-
+%%
+%% A generic Petri net OTP behavior.
+%%
+%% Copyright 2016-2017 Jorgen Brandt.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% -------------------------------------------------------------------
+%% @author Jorgen Brandt <joergen.brandt@onlinehome.de>
+%% @version 0.1.1
+%% @copyright 2016-2017 Jorgen Brandt.
+%% @doc Callback function definitions for Petri net structure definition.
+%%
+%% There are six callbacks that define the Petri net structure and its initial
+%% marking:
+%%
+%% <ul>
+%%   <li>`place_lst/0' returns the names of the places in the net</li>
+%%   <li>`trsn_lst/0' returns the names of the transitions in the net</li>
+%%   <li>`init_marking/1' returns the initial marking for a given place</li>
+%%   <li>`preset/1' returns the preset places of a given transition</li>
+%%   <li>`is_enabled/2' determines whether a given transition is enabled in a
+%%       given mode</li>
+%%   <li>`fire/2' returns which tokens are produced on what places if a given
+%%       transition is fired in a given mode that enables this transition</li>
+%% </ul>
+%%
+%% We have a look at each of them in turn.
+%%
+%% <h4>place_lst/0</h4>
+%%
+%% The `place_lst/0' function lets us define the names of all places in the net.
+%%
+%% Example:
+%% ```
+%% place_lst() ->
+%%   [coin_slot, cash_box, signal, storage, compartment].
+%% '''
+%% Here, we define the net to have the five places in the cookie vending
+%% machine.
+%%
+%% <h4>trsn_lst/0</h4>
+%%
+%% The `trsn_lst/0' function lets us define the names of all transitions in the
+%% net.
+%%
+%% Example:
+%% ```
+%% trsn_lst() ->
+%%   [a, b].
+%% '''
+%% Here, we define the net to have the two places `a' and `b' in the cookie
+%% vending machine.
+%%
+%% <h4>preset/1</h4>
+%%
+%% The `preset/1' lets us define the preset places of a given transition.
+%%
+%% Example:
+%% ```
+%% preset( a ) -> [coin_slot];
+%% preset( b ) -> [signal, storage].
+%% '''
+%% Here, we define the preset of the transition `a' to be just the place
+%% `coin_slot' while the transition `b' has the places `signal' and `storage'
+%% in its preset.
+%%
+%% <h4>init_marking/1</h4>
+%%
+%% The `init_marking/1' function lets us define the initial marking for a given
+%% place in the form of a token list.
+%%
+%% Example:
+%% ```
+%% init_marking( storage ) -> [cookie_box, cookie_box, cookie_box];
+%% init_marking( _ )       -> [].
+%% '''
+%% Here, we initialize the storage place with three `cookie_box` tokens. All
+%% other places are left empty.
+%%
+%% <h4>is_enabled/2</h4>
+%%
+%% The `is_enabled/2' function is a predicate determining whether a given
+%% transition is enabled in a given mode.
+%%
+%% Example:
+%% ```
+%% is_enabled( a, #{ coin_slot := [coin] } )                      -> true;
+%% is_enabled( b, #{ signal := [sig], storage := [cookie_box] } ) -> true;
+%% is_enabled( _, _ )                                             -> false.
+%% '''
+%% Here, we state that the transition `a' is enabled if it can consume a single
+%% `coin' from the `coin_slot' place. Similarly, the transition `b' is enabled
+%% if it can consume a `sig' token from the `signal' place and a `cookie_box'
+%% token from the `storage` place. No other configuration can enable a
+%% transition. E.g., managing to get a `button' token on the `coin_slot' place
+%% will not enable any transition.
+%%
+%% <h4>fire/2</h4>
+%%
+%% The `fire/2' function defines what tokens are produced when a given
+%% transition fires in a given mode. As arguments it takes the name of the
+%% transition, and a firing mode in the form of a hash map mapping place names
+%% to token lists. The `fire/2' function is called only on modes for which
+%% `is_enabled/2' returns `true'. The `fire/2' function is expected to return
+%% either a `{produce, ProduceMap}' tuple or the term `abort'. If `abort' is
+%% returned, the firing is aborted. Nothing is produced or consumed.
+%%
+%% Example:
+%% ```
+%% fire( a, _ ) -> {produce, #{ cash_box => [coin], signal => [sig] }};
+%% fire( b, _ ) -> {produce, #{ compartment => [cookie_box] }}.
+%% '''
+%% Here, the firing of the transition `a' produces a `coin' token on the
+%% `cash_box' place and a `sig' token on the `signal' place. Similarly, the
+%% firing of the transition `b' produces a `cookie_box' token on the
+%% `compartment' place. We do not need to state the tokens to be consumed
+%% because the firing mode already uniquely identifies the tokens to be
+%% consumed.
+%%
+%% @end
+%% -------------------------------------------------------------------
+
+
+-module( gen_pnet_struct ).
+
+-callback place_lst() -> [atom()].
+
+-callback trsn_lst() -> [atom()].
+
+-callback init_marking( atom() ) -> [_].
+
+-callback preset( Place :: atom() ) -> [atom()].
+
+-callback is_enabled( Trsn :: atom(), Mode :: #{ atom() => [_]} ) -> boolean().
+
+-callback fire( Trsn :: atom(), Mode :: #{ atom() => [_] } ) ->
+            abort | {produce, #{ atom() => [_] }}.