diff --git a/masque/builder/__init__.py b/masque/builder/__init__.py
index 1fabfbf..fc839cb 100644
--- a/masque/builder/__init__.py
+++ b/masque/builder/__init__.py
@@ -1,3 +1,4 @@
-from .builder import Builder, Abstract
+from .builder import Builder
+from .abstract import Abstract
 from .utils import ell
 from .tools import Tool
diff --git a/masque/builder/abstract.py b/masque/builder/abstract.py
new file mode 100644
index 0000000..8f4476d
--- /dev/null
+++ b/masque/builder/abstract.py
@@ -0,0 +1,59 @@
+from typing import Dict, Union, Optional
+from typing import MutableMapping, TYPE_CHECKING
+import copy
+import logging
+
+from ..pattern import Pattern
+from ..library import MutableLibrary
+from ..ports import PortList, Port
+from .tools import Tool
+
+if TYPE_CHECKING:
+    from .builder import Builder
+
+
+logger = logging.getLogger(__name__)
+
+
+class Abstract(PortList):
+    __slots__ = ('name', 'ports')
+
+    name: str
+    """ Name of the pattern this device references """
+
+    ports: Dict[str, Port]
+    """ Uniquely-named ports which can be used to snap instances together"""
+
+    def __init__(
+            self,
+            name: str,
+            ports: Dict[str, Port],
+            ) -> None:
+        self.name = name
+        self.ports = copy.deepcopy(ports)
+
+    def build(
+            self,
+            library: MutableLibrary,
+            tools: Union[None, Tool, MutableMapping[Optional[str], Tool]] = None,
+            ) -> 'Builder':
+        """
+        Begin building a new device around an instance of the current device
+          (rather than modifying the current device).
+
+        Returns:
+            The new `Builder` object.
+        """
+        pat = Pattern(ports=self.ports)
+        pat.ref(self.name)
+        new = Builder(library=library, pattern=pat, tools=tools)   # TODO should Ref have tools?
+        return new
+
+    # TODO do we want to store a Ref instead of just a name? then we can translate/rotate/mirror...
+
+    def __repr__(self) -> str:
+        s = f'<Abstract {self.name} ['
+        for name, port in self.ports.items():
+            s += f'\n\t{name}: {port}'
+        s += ']>'
+        return s
diff --git a/masque/builder/builder.py b/masque/builder/builder.py
index e4f0f87..77ccd70 100644
--- a/masque/builder/builder.py
+++ b/masque/builder/builder.py
@@ -14,6 +14,7 @@ from ..error import PortError, BuildError
 from ..ports import PortList, Port
 from .tools import Tool
 from .utils import ell
+from .abstract import Abstract
 
 
 logger = logging.getLogger(__name__)
@@ -22,50 +23,6 @@ logger = logging.getLogger(__name__)
 BB  = TypeVar('BB',  bound='Builder')
 
 
-class Abstract(PortList):
-    __slots__ = ('name', 'ports')
-
-    name: str
-    """ Name of the pattern this device references """
-
-    ports: Dict[str, Port]
-    """ Uniquely-named ports which can be used to snap instances together"""
-
-    def __init__(
-            self,
-            name: str,
-            ports: Dict[str, Port],
-            ) -> None:
-        self.name = name
-        self.ports = copy.deepcopy(ports)
-
-    def build(
-            self,
-            library: MutableLibrary,
-            tools: Union[None, Tool, MutableMapping[Optional[str], Tool]] = None,
-            ) -> 'Builder':
-        """
-        Begin building a new device around an instance of the current device
-          (rather than modifying the current device).
-
-        Returns:
-            The new `Builder` object.
-        """
-        pat = Pattern(ports=self.ports)
-        pat.ref(self.name)
-        new = Builder(library=library, pattern=pat, tools=tools)   # TODO should Ref have tools?
-        return new
-
-    # TODO do we want to store a Ref instead of just a name? then we can translate/rotate/mirror...
-
-    def __repr__(self) -> str:
-        s = f'<Abstract {self.name} ['
-        for name, port in self.ports.items():
-            s += f'\n\t{name}: {port}'
-        s += ']>'
-        return s
-
-
 class Builder(PortList):
     """
     TODO DOCUMENT Builder
diff --git a/masque/library.py b/masque/library.py
index cb44baf..1a707a2 100644
--- a/masque/library.py
+++ b/masque/library.py
@@ -19,10 +19,10 @@ from .error import LibraryError, PatternError
 from .utils import rotation_matrix_2d, normalize_mirror
 from .shapes import Shape, Polygon
 from .label import Label
+from .builder.abstract import Abstract
 
 if TYPE_CHECKING:
     from .pattern import Pattern
-    from .builder import Abstract
 
 
 logger = logging.getLogger(__name__)
@@ -42,7 +42,16 @@ class Library(Mapping[str, Pattern], metaclass=ABCMeta):
 
     #__contains__, keys, items, values, get, __eq__, __ne__ supplied by Mapping
 
-    def abstract(self, name: str) -> 'Abstract':
+    def abstract(self, name: str) -> Abstract:
+        """
+        Return an `Abstract` (name & ports) for the pattern in question.
+
+        Args:
+            name: The pattern name
+
+        Returns:
+            An `Abstract` object for the pattern
+        """
         return Abstract(name=name, ports=self[name].ports)
 
     def __repr__(self) -> str: