diff --git a/bonobo/_api.py b/bonobo/_api.py
index 5f08ae3..0df8594 100644
--- a/bonobo/_api.py
+++ b/bonobo/_api.py
@@ -10,7 +10,7 @@ to another is maximal.
 from bonobo.execution.strategies import create_strategy
 from bonobo.nodes import *
 from bonobo.nodes import __all__ as _all_nodes
-from bonobo.structs import Graph
+from bonobo.structs.graphs import Graph
 from bonobo.util.api import ApiHelper
 from bonobo.util.environ import parse_args, get_argument_parser
 from bonobo.registry import create_reader, create_writer
diff --git a/bonobo/constants.py b/bonobo/constants.py
index fde06de..056de9f 100644
--- a/bonobo/constants.py
+++ b/bonobo/constants.py
@@ -20,30 +20,13 @@
 
 
 """
-
-
-class Token:
-    def __init__(self, name):
-        self.__name__ = name
-
-    def __repr__(self):
-        return '<{}>'.format(self.__name__)
-
-
-class Flag(Token):
-    must_be_first = False
-    must_be_last = False
-    allows_data = True
-
+from bonobo.structs.tokens import Token
+from bonobo.util.envelopes import UnchangedEnvelope
 
 BEGIN = Token('Begin')
 END = Token('End')
 
-INHERIT = Flag('Inherit')
-NOT_MODIFIED = Flag('NotModified')
-NOT_MODIFIED.must_be_first = True
-NOT_MODIFIED.must_be_last = True
-NOT_MODIFIED.allows_data = False
+NOT_MODIFIED = UnchangedEnvelope()
 
 EMPTY = tuple()
 
diff --git a/bonobo/execution/contexts/graph.py b/bonobo/execution/contexts/graph.py
index ffc9dcc..59c9063 100644
--- a/bonobo/execution/contexts/graph.py
+++ b/bonobo/execution/contexts/graph.py
@@ -4,7 +4,7 @@ from queue import Empty
 from time import sleep
 
 from bonobo.config import create_container
-from bonobo.constants import BEGIN, END
+from bonobo.constants import BEGIN, END, EMPTY
 from bonobo.errors import InactiveReadableError
 from bonobo.execution import events
 from bonobo.execution.contexts.base import BaseContext
@@ -120,6 +120,10 @@ class GraphExecutionContext(BaseContext):
                 except InactiveReadableError:
                     nodes.discard(node)
 
+    def run_until_complete(self):
+        self.write(BEGIN, EMPTY, END)
+        self.loop()
+
     def stop(self, stopper=None):
         super(GraphExecutionContext, self).stop()
 
diff --git a/bonobo/execution/contexts/node.py b/bonobo/execution/contexts/node.py
index 44476f0..dd4d138 100644
--- a/bonobo/execution/contexts/node.py
+++ b/bonobo/execution/contexts/node.py
@@ -7,12 +7,14 @@ from types import GeneratorType
 
 from bonobo.config import create_container
 from bonobo.config.processors import ContextCurrifier
-from bonobo.constants import NOT_MODIFIED, BEGIN, END, TICK_PERIOD, Token, Flag, INHERIT
+from bonobo.constants import BEGIN, END, TICK_PERIOD
 from bonobo.errors import InactiveReadableError, UnrecoverableError, UnrecoverableTypeError
 from bonobo.execution.contexts.base import BaseContext
 from bonobo.structs.inputs import Input
-from bonobo.util import get_name, isconfigurabletype, ensure_tuple
+from bonobo.structs.tokens import Token, Flag
+from bonobo.util import get_name, isconfigurabletype, ensure_tuple, deprecated
 from bonobo.util.bags import BagType
+from bonobo.util.envelopes import isenvelope, F_NOT_MODIFIED, F_INHERIT
 from bonobo.util.statistics import WithStatistics
 
 logger = logging.getLogger(__name__)
@@ -329,17 +331,29 @@ class NodeExecutionContext(BaseContext, WithStatistics):
         :return: Bag
         """
 
-        tokens, _output = split_token(_output)
+        if isenvelope(_output):
+            _output, _flags, _options = _output.unfold()
+        else:
+            _flags, _options = [], {}
 
-        if NOT_MODIFIED in tokens:
-            return ensure_tuple(_input, cls=(self.output_type or tuple))
+        if len(_flags):
+            # TODO: parse flags to check constraints are respected (like not modified alone, etc.)
 
-        if INHERIT in tokens:
-            if self._output_type is None:
-                self._output_type = concat_types(self._input_type, self._input_length, self._output_type, len(_output))
-            _output = _input + ensure_tuple(_output)
+            if F_NOT_MODIFIED in _flags:
+                return _input
 
-        return ensure_tuple(_output, cls=(self._output_type or tuple))
+            if F_INHERIT in _flags:
+                if self._output_type is None:
+                    self._output_type = concat_types(
+                        self._input_type, self._input_length, self._output_type, len(_output)
+                    )
+                _output = _input + ensure_tuple(_output)
+
+        if not self._output_type:
+            if issubclass(type(_output), tuple):
+                self._output_type = type(_output)
+
+        return ensure_tuple(_output, cls=self._output_type)
 
     def _send(self, value, _control=False):
         """
@@ -367,6 +381,7 @@ def isflag(param):
     return isinstance(param, Flag)
 
 
+@deprecated
 def split_token(output):
     """
     Split an output into token tuple, real output tuple.
@@ -392,6 +407,7 @@ def split_token(output):
     output = output[i:]
     if not data_allowed and len(output):
         raise ValueError('Output data provided after a flag that does not allow data.')
+
     return flags, output
 
 
diff --git a/bonobo/structs/__init__.py b/bonobo/structs/__init__.py
index ba640c9..e69de29 100644
--- a/bonobo/structs/__init__.py
+++ b/bonobo/structs/__init__.py
@@ -1,5 +0,0 @@
-from bonobo.structs.graphs import Graph
-
-__all__ = [
-    'Graph',
-]
diff --git a/bonobo/structs/tokens.py b/bonobo/structs/tokens.py
new file mode 100644
index 0000000..9b8f151
--- /dev/null
+++ b/bonobo/structs/tokens.py
@@ -0,0 +1,12 @@
+class Token:
+    def __init__(self, name):
+        self.__name__ = name
+
+    def __repr__(self):
+        return '<{}>'.format(self.__name__)
+
+
+class Flag(Token):
+    must_be_first = False
+    must_be_last = False
+    allows_data = True
diff --git a/bonobo/util/collections.py b/bonobo/util/collections.py
index 1f72e8c..1234142 100644
--- a/bonobo/util/collections.py
+++ b/bonobo/util/collections.py
@@ -3,7 +3,17 @@ import functools
 
 
 class sortedlist(list):
+    """
+    A list with an insort() method that wan be used to maintain sorted lists. The list by itself is not sorted, it's
+    up to the user to not insert unsorted elements.
+    """
+
     def insort(self, x):
+        """
+        If the list is sorted, insert the element in the right place. Otherwise, unpredictable behaviour.
+
+        :param x:
+        """
         bisect.insort(self, x)
 
 
diff --git a/bonobo/util/envelopes.py b/bonobo/util/envelopes.py
new file mode 100644
index 0000000..04f8080
--- /dev/null
+++ b/bonobo/util/envelopes.py
@@ -0,0 +1,32 @@
+from bonobo.structs.tokens import Flag
+
+F_INHERIT = Flag('Inherit')
+
+F_NOT_MODIFIED = Flag('NotModified')
+F_NOT_MODIFIED.must_be_first = True
+F_NOT_MODIFIED.must_be_last = True
+F_NOT_MODIFIED.allows_data = False
+
+
+class Envelope:
+    def __init__(self, content, *, flags=None, **options):
+        self._content = content
+        self._flags = set(flags or ())
+        self._options = options
+
+    def unfold(self):
+        return self._content, self._flags, self._options
+
+
+class AppendingEnvelope(Envelope):
+    def __init__(self, content, **options):
+        super().__init__(content, flags={F_INHERIT}, **options)
+
+
+class UnchangedEnvelope(Envelope):
+    def __init__(self, **options):
+        super().__init__(None, flags={F_NOT_MODIFIED}, **options)
+
+
+def isenvelope(mixed):
+    return isinstance(mixed, Envelope)
diff --git a/bonobo/util/testing.py b/bonobo/util/testing.py
index 8000e89..19dd472 100644
--- a/bonobo/util/testing.py
+++ b/bonobo/util/testing.py
@@ -11,7 +11,7 @@ import pytest
 
 from bonobo import open_fs, __main__, get_examples_path
 from bonobo.commands import entrypoint
-from bonobo.constants import Token
+from bonobo.structs.tokens import Token
 from bonobo.execution.contexts.graph import GraphExecutionContext
 from bonobo.execution.contexts.node import NodeExecutionContext
 
diff --git a/tests/examples/test_example_change_some_fields.py b/tests/examples/test_example_change_some_fields.py
new file mode 100644
index 0000000..8fd5ff0
--- /dev/null
+++ b/tests/examples/test_example_change_some_fields.py
@@ -0,0 +1,62 @@
+from collections import namedtuple
+
+import bonobo
+from bonobo.config import use_raw_input
+from bonobo.execution.contexts import GraphExecutionContext
+from bonobo.util.bags import BagType
+
+Extracted = namedtuple('Extracted', ['id', 'name', 'value'])
+ExtractedBT = BagType('ExtractedBT', ['id', 'name', 'value'])
+
+
+def extract_nt():
+    yield Extracted(id=1, name='Guido', value='.py')
+    yield Extracted(id=2, name='Larry', value='.pl')
+    yield Extracted(id=3, name='Dennis', value='.c')
+    yield Extracted(id=4, name='Yukihiro', value='.rb')
+
+
+def extract_bt():
+    yield ExtractedBT(id=1, name='Guido', value='.py')
+    yield ExtractedBT(id=2, name='Larry', value='.pl')
+    yield ExtractedBT(id=3, name='Dennis', value='.c')
+    yield ExtractedBT(id=4, name='Yukihiro', value='.rb')
+
+
+def transform_using_args(id, name, value):
+    yield Extracted(id=id * 2, name=name, value=name.lower() + value)
+
+
+@use_raw_input
+def transform_nt(row):
+    yield row._replace(name=row.name.upper())
+
+
+def StoreInList(buffer: list):
+    def store_in_list(*args, buffer=buffer):
+        buffer.append(args)
+
+    return store_in_list
+
+
+def test_execution():
+    graph = bonobo.Graph()
+
+    result_args = []
+    result_nt = []
+    result_bt = []
+
+    graph.add_chain(extract_nt, transform_using_args, StoreInList(result_args))
+    graph.add_chain(transform_nt, StoreInList(result_nt), _input=extract_nt)
+    graph.add_chain(extract_bt, transform_using_args, StoreInList(result_bt))
+
+    with GraphExecutionContext(graph) as context:
+        context.run_until_complete()
+
+    assert result_args == [(2, 'Guido', 'guido.py'), (4, 'Larry', 'larry.pl'), (6, 'Dennis', 'dennis.c'),
+                           (8, 'Yukihiro', 'yukihiro.rb')]
+
+    assert result_nt == [(1, 'GUIDO', '.py'), (2, 'LARRY', '.pl'), (3, 'DENNIS', '.c'), (4, 'YUKIHIRO', '.rb')]
+
+    assert result_bt == [(2, 'Guido', 'guido.py'), (4, 'Larry', 'larry.pl'), (6, 'Dennis', 'dennis.c'),
+                         (8, 'Yukihiro', 'yukihiro.rb')]
diff --git a/tests/execution/contexts/test_execution_contexts_node.py b/tests/execution/contexts/test_execution_contexts_node.py
index 5af665d..ca9de41 100644
--- a/tests/execution/contexts/test_execution_contexts_node.py
+++ b/tests/execution/contexts/test_execution_contexts_node.py
@@ -3,9 +3,10 @@ from unittest.mock import MagicMock
 import pytest
 
 from bonobo import Graph
-from bonobo.constants import EMPTY, NOT_MODIFIED, INHERIT
+from bonobo.constants import EMPTY
 from bonobo.execution.contexts.node import NodeExecutionContext, split_token
 from bonobo.execution.strategies import NaiveStrategy
+from bonobo.util.envelopes import F_NOT_MODIFIED, F_INHERIT
 from bonobo.util.testing import BufferingNodeExecutionContext, BufferingGraphExecutionContext
 
 
@@ -227,32 +228,36 @@ def test_node_lifecycle_with_kill():
 
 
 def test_split_token():
-    assert split_token(('foo', 'bar')) == (set(), ('foo', 'bar'))
-    assert split_token(()) == (set(), ())
-    assert split_token('') == (set(), ('', ))
+    with pytest.deprecated_call():
+        assert split_token(('foo', 'bar')) == (set(), ('foo', 'bar'))
+        assert split_token(()) == (set(), ())
+        assert split_token('') == (set(), ('', ))
 
 
 def test_split_token_duplicate():
-    with pytest.raises(ValueError):
-        split_token((NOT_MODIFIED, NOT_MODIFIED))
-    with pytest.raises(ValueError):
-        split_token((INHERIT, INHERIT))
-    with pytest.raises(ValueError):
-        split_token((INHERIT, NOT_MODIFIED, INHERIT))
+    with pytest.deprecated_call():
+        with pytest.raises(ValueError):
+            split_token((F_NOT_MODIFIED, F_NOT_MODIFIED))
+        with pytest.raises(ValueError):
+            split_token((F_INHERIT, F_INHERIT))
+        with pytest.raises(ValueError):
+            split_token((F_INHERIT, F_NOT_MODIFIED, F_INHERIT))
 
 
 def test_split_token_not_modified():
-    with pytest.raises(ValueError):
-        split_token((NOT_MODIFIED, 'foo', 'bar'))
-    with pytest.raises(ValueError):
-        split_token((NOT_MODIFIED, INHERIT))
-    with pytest.raises(ValueError):
-        split_token((INHERIT, NOT_MODIFIED))
-    assert split_token(NOT_MODIFIED) == ({NOT_MODIFIED}, ())
-    assert split_token((NOT_MODIFIED, )) == ({NOT_MODIFIED}, ())
+    with pytest.deprecated_call():
+        with pytest.raises(ValueError):
+            split_token((F_NOT_MODIFIED, 'foo', 'bar'))
+        with pytest.raises(ValueError):
+            split_token((F_NOT_MODIFIED, F_INHERIT))
+        with pytest.raises(ValueError):
+            split_token((F_INHERIT, F_NOT_MODIFIED))
+        assert split_token(F_NOT_MODIFIED) == ({F_NOT_MODIFIED}, ())
+        assert split_token((F_NOT_MODIFIED, )) == ({F_NOT_MODIFIED}, ())
 
 
 def test_split_token_inherit():
-    assert split_token(INHERIT) == ({INHERIT}, ())
-    assert split_token((INHERIT, )) == ({INHERIT}, ())
-    assert split_token((INHERIT, 'foo', 'bar')) == ({INHERIT}, ('foo', 'bar'))
+    with pytest.deprecated_call():
+        assert split_token(F_INHERIT) == ({F_INHERIT}, ())
+        assert split_token((F_INHERIT, )) == ({F_INHERIT}, ())
+        assert split_token((F_INHERIT, 'foo', 'bar')) == ({F_INHERIT}, ('foo', 'bar'))
diff --git a/tests/features/test_inherit.py b/tests/features/test_inherit.py
index 92b943b..63c6a5d 100644
--- a/tests/features/test_inherit.py
+++ b/tests/features/test_inherit.py
@@ -1,4 +1,4 @@
-from bonobo.constants import INHERIT
+from bonobo.util.envelopes import AppendingEnvelope
 from bonobo.util.testing import BufferingNodeExecutionContext
 
 messages = [
@@ -8,7 +8,7 @@ messages = [
 
 
 def append(*args):
-    return INHERIT, '!'
+    return AppendingEnvelope('!')
 
 
 def test_inherit():
diff --git a/tests/features/test_not_modified.py b/tests/features/test_not_modified.py
index 20f6f96..63b27d8 100644
--- a/tests/features/test_not_modified.py
+++ b/tests/features/test_not_modified.py
@@ -15,4 +15,6 @@ def test_not_modified():
     with BufferingNodeExecutionContext(useless) as context:
         context.write_sync(*input_messages)
 
-    assert context.get_buffer() == input_messages
+    result = context.get_buffer()
+    print(result)
+    assert result == input_messages
diff --git a/tests/nodes/test_casts.py b/tests/nodes/test_casts.py
new file mode 100644
index 0000000..3eb3621
--- /dev/null
+++ b/tests/nodes/test_casts.py
@@ -0,0 +1,65 @@
+from collections import namedtuple
+from typing import Callable
+
+import pytest
+
+from bonobo.constants import EMPTY
+from bonobo.util.bags import BagType
+from bonobo.util.envelopes import Envelope
+from bonobo.util.testing import BufferingNodeExecutionContext
+
+MyTuple = namedtuple('MyTuple', ['a', 'b', 'c'])
+MyBag = BagType('MyBag', ['a', 'b', 'c'])
+
+
+class MyCustomType():
+    def __init__(self, *args):
+        self.args = args
+
+    def as_tuple(self):
+        return MyBag(*self.args)
+
+
+@pytest.mark.parametrize(['factory', 'expected', 'expected_item0'], [
+    [lambda: (1, 2, 3), tuple, int],
+    [lambda: Envelope((1, 2, 3)), tuple, int],
+    [lambda: MyTuple(1, 2, 3), MyTuple, int],
+    [lambda: Envelope(MyTuple(1, 2, 3)), MyTuple, int],
+    [lambda: MyBag(1, 2, 3), MyBag, int],
+    [lambda: Envelope(MyBag(1, 2, 3)), MyBag, int],
+    [lambda: MyCustomType(1, 2, 3), tuple, MyCustomType],
+    [lambda: Envelope(MyCustomType(1, 2, 3)), tuple, MyCustomType],
+])
+def test_casts_after_output(factory: Callable, expected, expected_item0):
+    def transform():
+        yield factory()
+        yield factory()
+
+    with BufferingNodeExecutionContext(transform) as context:
+        context.write_sync(EMPTY)
+
+    result = context.get_buffer()
+    assert expected == type(result[0])
+    assert expected_item0 == type(result[0][0])
+    assert expected == type(result[1])
+    assert expected_item0 == type(result[1][0])
+
+
+def test_cast_after_returning_custom_type():
+    def transform():
+        yield MyCustomType(1, 2, 3)
+        yield MyCustomType(4, 5, 6)
+
+    with BufferingNodeExecutionContext(transform) as context:
+        context.write_sync(EMPTY)
+    result = context.get_buffer()
+    assert tuple == type(result[0])
+    assert tuple == type(result[1])
+    assert MyCustomType == type(result[0][0])
+    assert MyCustomType == type(result[1][0])
+
+    with BufferingNodeExecutionContext(MyCustomType.as_tuple) as context:
+        context.write_sync(*result)
+    result = context.get_buffer()
+    assert MyBag == type(result[0])
+    assert MyBag == type(result[1])
diff --git a/tests/structs/test_graphs.py b/tests/structs/test_graphs.py
index 7f3a58d..51321ae 100644
--- a/tests/structs/test_graphs.py
+++ b/tests/structs/test_graphs.py
@@ -3,7 +3,7 @@ import pytest
 from unittest.mock import sentinel
 
 from bonobo.constants import BEGIN
-from bonobo.structs import Graph
+from bonobo.structs.graphs import Graph
 
 identity = lambda x: x
 
diff --git a/tests/structs/test_tokens.py b/tests/structs/test_tokens.py
index e66b796..6bd9bee 100644
--- a/tests/structs/test_tokens.py
+++ b/tests/structs/test_tokens.py
@@ -1,4 +1,4 @@
-from bonobo.constants import Token
+from bonobo.structs.tokens import Token
 
 
 def test_token_repr():
diff --git a/tests/test_execution.py b/tests/test_execution.py
index 92cd30c..3f51c45 100644
--- a/tests/test_execution.py
+++ b/tests/test_execution.py
@@ -2,7 +2,7 @@ from bonobo.config.processors import use_context_processor
 from bonobo.constants import BEGIN, END
 from bonobo.execution.contexts.graph import GraphExecutionContext
 from bonobo.execution.strategies import NaiveStrategy
-from bonobo.structs import Graph
+from bonobo.structs.graphs import Graph
 
 
 def generate_integers():