diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index c74a17dc..acd8393e 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -70,7 +70,7 @@ jobs:
 
       - run: |
           mk python-release owner=vkottler \
-                            repo=runtimepy version=2.1.2
+                            repo=runtimepy version=2.1.3
         if: |
           matrix.python-version == '3.11'
           && matrix.system == 'ubuntu-latest'
diff --git a/.pylintrc b/.pylintrc
index be2a5a69..f84bb969 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -1,5 +1,5 @@
 [DESIGN]
-max-args=7
+max-args=8
 max-attributes=12
 max-parents=8
 
diff --git a/README.md b/README.md
index ce3620a3..ac83de95 100644
--- a/README.md
+++ b/README.md
@@ -2,11 +2,11 @@
     =====================================
     generator=datazen
     version=3.1.2
-    hash=64a758df8095e218dce93935454221a7
+    hash=6a75e29b42b1d2fa20b1373c2a8adc01
     =====================================
 -->
 
-# runtimepy ([2.1.2](https://pypi.org/project/runtimepy/))
+# runtimepy ([2.1.3](https://pypi.org/project/runtimepy/))
 
 [![python](https://img.shields.io/pypi/pyversions/runtimepy.svg)](https://pypi.org/project/runtimepy/)
 ![Build Status](https://github.com/vkottler/runtimepy/workflows/Python%20Package/badge.svg)
diff --git a/local/variables/package.yaml b/local/variables/package.yaml
index 0841c680..254e6e35 100644
--- a/local/variables/package.yaml
+++ b/local/variables/package.yaml
@@ -1,5 +1,5 @@
 ---
 major: 2
 minor: 1
-patch: 2
+patch: 3
 entry: runtimepy
diff --git a/pyproject.toml b/pyproject.toml
index 40377b50..0714556e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta:__legacy__"
 
 [project]
 name = "runtimepy"
-version = "2.1.2"
+version = "2.1.3"
 description = "A framework for implementing Python services."
 readme = "README.md"
 requires-python = ">=3.8"
diff --git a/runtimepy/__init__.py b/runtimepy/__init__.py
index f7744741..118eb9dd 100644
--- a/runtimepy/__init__.py
+++ b/runtimepy/__init__.py
@@ -1,7 +1,7 @@
 # =====================================
 # generator=datazen
 # version=3.1.2
-# hash=f83181278a252952c4fdf15493634816
+# hash=933cfe7057a94bf7e43e8b9938cb8159
 # =====================================
 
 """
@@ -10,4 +10,4 @@
 
 DESCRIPTION = "A framework for implementing Python services."
 PKG_NAME = "runtimepy"
-VERSION = "2.1.2"
+VERSION = "2.1.3"
diff --git a/runtimepy/codec/protocol/base.py b/runtimepy/codec/protocol/base.py
index bea2fdfe..9a1361ed 100644
--- a/runtimepy/codec/protocol/base.py
+++ b/runtimepy/codec/protocol/base.py
@@ -29,6 +29,7 @@
 from runtimepy.primitives.byte_order import ByteOrder as _ByteOrder
 from runtimepy.primitives.field.fields import BitFields as _BitFields
 from runtimepy.primitives.field.manager import BitFieldsManager
+from runtimepy.primitives.serializable import Serializable, SerializableMap
 from runtimepy.registry.name import NameRegistry as _NameRegistry
 from runtimepy.registry.name import RegistryKey as _RegistryKey
 
@@ -68,6 +69,7 @@ def __init__(
         build: _List[_Union[int, FieldSpec]] = None,
         identifier: int = 1,
         byte_order: _Union[_ByteOrder, _RegistryKey] = _DEFAULT_BYTE_ORDER,
+        serializables: SerializableMap = None,
     ) -> None:
         """Initialize this protocol."""
 
@@ -110,6 +112,12 @@ def __init__(
                     item.name, item.kind, enum=item.enum, track=False
                 )
 
+        # Keep track of named serializables.
+        self.serializables: SerializableMap = {}
+        if serializables is not None:
+            for name, serializable in serializables.items():
+                self.add_field(name, serializable=serializable)
+
     def __copy__(self: T) -> T:
         """Create another protocol instance from this one."""
 
@@ -119,6 +127,7 @@ def __copy__(self: T) -> T:
             fields=_copy(self._fields),
             build=self._build,
             byte_order=self.array.byte_order,
+            serializables=self.serializables,
         )
 
     def add_field(
@@ -126,6 +135,7 @@ def add_field(
         name: str,
         kind: _Primitivelike = None,
         enum: _RegistryKey = None,
+        serializable: Serializable = None,
         track: bool = True,
     ) -> None:
         """Add a new field to the protocol."""
@@ -134,10 +144,21 @@ def add_field(
         ident = self._names.register_name(name)
         assert ident is not None, f"Couldn't register field '{name}'!"
 
+        # Add the serializable to the end of this protocol.
+        if serializable is not None:
+            assert kind is None and enum is None
+            self.serializables[name] = serializable
+            self.array.add_to_end(serializable)
+            return
+
         if enum is not None:
             runtime_enum = self._enum_registry[enum]
             self._enum_fields[name] = runtime_enum
-            kind = runtime_enum.primitive
+
+            # Allow the primitive type to be overridden when passed as a
+            # method argument.
+            if kind is None:
+                kind = runtime_enum.primitive
 
         assert kind is not None
         new = _create(kind)
diff --git a/runtimepy/data/schemas/RuntimeEnum.yaml b/runtimepy/data/schemas/RuntimeEnum.yaml
index 7bcb2a75..30d3f46c 100644
--- a/runtimepy/data/schemas/RuntimeEnum.yaml
+++ b/runtimepy/data/schemas/RuntimeEnum.yaml
@@ -23,5 +23,4 @@ properties:
       "^\\w+$":
         oneOf:
           - type: integer
-            minimum: 0
           - type: boolean
diff --git a/runtimepy/primitives/array/__init__.py b/runtimepy/primitives/array/__init__.py
index 3e34a569..59f81f73 100644
--- a/runtimepy/primitives/array/__init__.py
+++ b/runtimepy/primitives/array/__init__.py
@@ -39,7 +39,7 @@ def __init__(
         *primitives: _AnyPrimitive,
         byte_order: _ByteOrder = _DEFAULT_BYTE_ORDER,
         fragments: _List[ArrayFragmentSpec] = None,
-        next_array: "PrimitiveArray" = None,
+        chain: Serializable = None,
     ) -> None:
         """Initialize this primitive array."""
 
@@ -59,7 +59,7 @@ def __init__(
         for item in primitives:
             self.add(item)
 
-        super().__init__(byte_order=self.byte_order, chain=next_array)
+        super().__init__(byte_order=self.byte_order, chain=chain)
 
         self._fragments: _List["PrimitiveArray"] = []
         self._fragment_specs: _List[ArrayFragmentSpec] = []
diff --git a/runtimepy/primitives/serializable/__init__.py b/runtimepy/primitives/serializable/__init__.py
index 803ffd15..4630386c 100644
--- a/runtimepy/primitives/serializable/__init__.py
+++ b/runtimepy/primitives/serializable/__init__.py
@@ -2,8 +2,13 @@
 A module defining an interface for serializable objects.
 """
 
+# built-in
+from typing import Dict
+
 # internal
 from runtimepy.primitives.serializable.base import Serializable
 from runtimepy.primitives.serializable.fixed import FixedChunk
+from runtimepy.primitives.serializable.prefixed import PrefixedChunk
 
-__all__ = ["Serializable", "FixedChunk"]
+SerializableMap = Dict[str, Serializable]
+__all__ = ["Serializable", "SerializableMap", "FixedChunk", "PrefixedChunk"]
diff --git a/tests/codec/test_protocol.py b/tests/codec/test_protocol.py
index 2931cf2e..95a4074a 100644
--- a/tests/codec/test_protocol.py
+++ b/tests/codec/test_protocol.py
@@ -11,6 +11,7 @@
 from runtimepy.codec.protocol import Protocol
 from runtimepy.codec.protocol.base import FieldSpec
 from runtimepy.enum.registry import EnumRegistry
+from runtimepy.primitives.serializable import PrefixedChunk
 
 # internal
 from tests.resources import resource
@@ -62,3 +63,16 @@ def test_protocol_basic():
         assert Protocol.import_json(load(stream))
 
     assert str(proto)
+
+    # Create a string serializable.
+    string = PrefixedChunk.create()
+    assert string.length() == 2
+    assert string.update_str("abc") == 5
+
+    # Add the string to the end and confirm the size update.
+    curr = proto.size
+    proto.add_field("string", serializable=string)
+    assert proto.size == curr + 5
+
+    # Should be the same size.
+    assert copy(proto).size == proto.size