diff --git a/masque/abstract.py b/masque/abstract.py
index 9b06d1c..e1202bf 100644
--- a/masque/abstract.py
+++ b/masque/abstract.py
@@ -3,11 +3,13 @@ from typing import Dict, TypeVar
 import copy
 import logging
 
+import numpy
 from numpy.typing import ArrayLike
 
 #from .pattern import Pattern
 from .ref import Ref
 from .ports import PortList, Port
+from .utils import rotation_matrix_2d, normalize_mirror
 
 #if TYPE_CHECKING:
 #    from .builder import Builder, Tool
@@ -203,7 +205,7 @@ class Abstract(PortList):
         Returns:
             self
         """
-        mirror_across_x, angle = normalize_mirror(ref.mirrored)
+        mirrored_across_x, angle = normalize_mirror(ref.mirrored)
         if mirrored_across_x:
             self.mirror(across_axis=0)
         self.rotate_ports(angle + ref.rotation)
@@ -224,7 +226,7 @@ class Abstract(PortList):
 
         # TODO test undo_ref_transform
         """
-        mirror_across_x, angle = normalize_mirror(ref.mirrored)
+        mirrored_across_x, angle = normalize_mirror(ref.mirrored)
         self.translate_ports(-ref.offset)
         self.rotate_port_offsets(-angle - ref.rotation)
         self.rotate_ports(-angle - ref.rotation)
diff --git a/masque/builder/builder.py b/masque/builder/builder.py
index c33a3ef..530c079 100644
--- a/masque/builder/builder.py
+++ b/masque/builder/builder.py
@@ -13,6 +13,7 @@ from ..library import MutableLibrary
 from ..error import PortError, BuildError
 from ..ports import PortList, Port
 from ..abstract import Abstract
+from ..utils import SupportsBool
 from .tools import Tool
 from .utils import ell
 
@@ -148,7 +149,7 @@ class Builder(PortList):
     @classmethod
     def interface(
             cls,
-            source: Union[PortList, Mapping[str, Port]],
+            source: Union[PortList, Mapping[str, Port], str],
             *,
             library: Optional[MutableLibrary] = None,
             tools: Union[None, Tool, MutableMapping[Optional[str], Tool]] = None,
@@ -215,7 +216,9 @@ class Builder(PortList):
         if tools is None and hasattr(source, 'tools') and isinstance(source.tools, dict):
             tools = source.tools
 
-        if isinstance(source, PortList):
+        if isinstance(source, str):
+            orig_ports = library.abstract(source).ports
+        elif isinstance(source, PortList):
             orig_ports = source.ports
         elif isinstance(source, dict):
             orig_ports = source
@@ -250,7 +253,7 @@ class Builder(PortList):
 
     def plug(
             self: BB,
-            other: Abstract,
+            other: Union[Abstract, str],
             map_in: Dict[str, str],
             map_out: Optional[Dict[str, Optional[str]]] = None,
             *,
@@ -280,7 +283,7 @@ class Builder(PortList):
             having to provide `map_out` each time `plug` is called.
 
         Args:
-            other: A `DeviceRef` describing the device to be instatiated.
+            other: An `Abstract` describing the device to be instatiated.
             map_in: Dict of `{'self_port': 'other_port'}` mappings, specifying
                 port connections between the two devices.
             map_out: Dict of `{'old_name': 'new_name'}` mappings, specifying
@@ -315,6 +318,9 @@ class Builder(PortList):
             logger.error('Skipping plug() since device is dead')
             return self
 
+        if isinstance(other, str):
+            other = self.library.abstract(other)
+
         if (inherit_name
                 and not map_out
                 and len(map_in) == 1
@@ -345,7 +351,7 @@ class Builder(PortList):
 
     def place(
             self: BB,
-            other: Abstract,
+            other: Union[Abstract, str],
             *,
             offset: ArrayLike = (0, 0),
             rotation: float = 0,
@@ -369,7 +375,7 @@ class Builder(PortList):
             rather than the port name on the original `pad` device.
 
         Args:
-            other: A `DeviceRef` describing the device to be instatiated.
+            other: An `Abstract` describing the device to be instatiated.
             offset: Offset at which to place the instance. Default (0, 0).
             rotation: Rotation applied to the instance before placement. Default 0.
             pivot: Rotation is applied around this pivot point (default (0, 0)).
@@ -395,6 +401,9 @@ class Builder(PortList):
             logger.error('Skipping place() since device is dead')
             return self
 
+        if isinstance(other, str):
+            other = self.library.abstract(other)
+
         if port_map is None:
             port_map = {}
 
@@ -508,7 +517,7 @@ class Builder(PortList):
     def path(
             self: BB,
             portspec: str,
-            ccw: Optional[bool],
+            ccw: Optional[SupportsBool],
             length: float,
             *,
             tool_port_names: Sequence[str] = ('A', 'B'),
@@ -529,7 +538,7 @@ class Builder(PortList):
     def path_to(
             self: BB,
             portspec: str,
-            ccw: Optional[bool],
+            ccw: Optional[SupportsBool],
             position: float,
             *,
             tool_port_names: Sequence[str] = ('A', 'B'),
@@ -563,7 +572,7 @@ class Builder(PortList):
     def mpath(
             self: BB,
             portspec: Union[str, Sequence[str]],
-            ccw: Optional[bool],
+            ccw: Optional[SupportsBool],
             *,
             spacing: Optional[Union[float, ArrayLike]] = None,
             set_rotation: Optional[float] = None,
@@ -611,4 +620,13 @@ class Builder(PortList):
 
     # TODO def path_join() and def bus_join()?
 
+    def flatten(self: BB) -> BB:
+        """
+        Flatten the contained pattern, using the contained library to resolve references.
+
+        Returns:
+            self
+        """
+        self.pattern.flatten(self.library)
+        return self
 
diff --git a/masque/builder/port_utils.py b/masque/builder/port_utils.py
index 5a1d5e9..2ee9a35 100644
--- a/masque/builder/port_utils.py
+++ b/masque/builder/port_utils.py
@@ -5,15 +5,14 @@ Functions for writing port data into a Pattern (`dev2pat`) and retrieving it (`p
 the port locations. This particular approach is just a sensible default; feel free to
 to write equivalent functions for your own format or alternate storage methods.
 """
-from typing import Sequence, Optional, Mapping, Tuple, Dict
+from typing import Sequence, Optional, Mapping
 import logging
 
 import numpy
-from numpy.typing import NDArray
 
 from ..pattern import Pattern
 from ..label import Label
-from ..utils import rotation_matrix_2d, layer_t
+from ..utils import layer_t
 from ..ports import Port
 from ..error import PatternError
 from ..library import Library, WrapROLibrary
@@ -79,7 +78,6 @@ def pat2dev(
             to contain their own port info without interfering with supercells'
             port data.
             Default True.
-        blacklist: If a cell name appears in the blacklist, do not ea
 
     Returns:
         The updated `pattern`. Port labels are not removed.
@@ -99,6 +97,8 @@ def pat2dev(
     # Load ports for all subpatterns, and use any we find
     found_ports = False
     for target in set(rr.target for rr in pattern.refs):
+        if target is None:
+            continue
         pp = pat2dev(
             layers=layers,
             library=library,
@@ -106,7 +106,6 @@ def pat2dev(
             name=target,
             max_depth=max_depth - 1,
             skip_subcells=skip_subcells,
-            blacklist=blacklist + {name},
             )
         found_ports |= bool(pp.ports)
 
@@ -114,6 +113,8 @@ def pat2dev(
         return pattern
 
     for ref in pattern.refs:
+        if ref.target is None:
+            continue
         aa = library.abstract(ref.target)
         if not aa.ports:
             continue
diff --git a/masque/builder/tools.py b/masque/builder/tools.py
index 1239100..71f1062 100644
--- a/masque/builder/tools.py
+++ b/masque/builder/tools.py
@@ -3,6 +3,8 @@ Tools are objects which dynamically generate simple single-use devices (e.g. wir
 """
 from typing import TYPE_CHECKING, Optional, Sequence
 
+from ..utils import SupportsBool
+
 if TYPE_CHECKING:
     from ..pattern import Pattern
 
@@ -10,7 +12,7 @@ if TYPE_CHECKING:
 class Tool:
     def path(
             self,
-            ccw: Optional[bool],
+            ccw: Optional[SupportsBool],
             length: float,
             *,
             in_ptype: Optional[str] = None,
diff --git a/masque/builder/utils.py b/masque/builder/utils.py
index d04caff..67c999a 100644
--- a/masque/builder/utils.py
+++ b/masque/builder/utils.py
@@ -6,7 +6,7 @@ import numpy
 from numpy import pi
 from numpy.typing import ArrayLike, NDArray
 
-from ..utils import rotation_matrix_2d
+from ..utils import rotation_matrix_2d, SupportsBool
 from ..error import BuildError
 
 if TYPE_CHECKING:
@@ -15,7 +15,7 @@ if TYPE_CHECKING:
 
 def ell(
         ports: Mapping[str, 'Port'],
-        ccw: Optional[bool],
+        ccw: Optional[SupportsBool],
         bound_type: str,
         bound: Union[float, ArrayLike],
         *,
diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index aff2da6..ac31360 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -571,7 +571,7 @@ def load_libraryfile(
         *,
         use_mmap: bool = True,
         full_load: bool = False,
-        postprocess: Optional[Callable[[Library, str], Pattern]] = None
+        postprocess: Optional[Callable[[Library, str, Pattern], Pattern]] = None
         ) -> Tuple[LazyLibrary, Dict[str, Any]]:
     """
     Wrapper for `load_library()` that takes a filename or path instead of a stream.
diff --git a/masque/library.py b/masque/library.py
index bd2857d..b7318f8 100644
--- a/masque/library.py
+++ b/masque/library.py
@@ -5,7 +5,7 @@ Library classes for managing unique name->pattern mappings and
 # TODO documentn all library classes
 # TODO toplevel documentation of library, classes, and abstracts
 """
-from typing import List, Dict, Callable, TypeVar, Generic, Type, TYPE_CHECKING
+from typing import List, Dict, Callable, TypeVar, Generic, Type, TYPE_CHECKING, cast
 from typing import Tuple, Union, Iterator, Mapping, MutableMapping, Set, Optional, Sequence
 import logging
 import base64
@@ -396,14 +396,14 @@ class Library(Mapping[str, 'Pattern'], metaclass=ABCMeta):
 
         if pattern is not original_pattern:
             name = hierarchy[-1]
-            if not isintance(self, MutableLibrary):
+            if not isinstance(self, MutableLibrary):
                 raise LibraryError('visit_* functions returned a new `Pattern` object'
                                    ' but the library is immutable')
             if name is None:
                 raise LibraryError('visit_* functions returned a new `Pattern` object'
                                    ' but no top-level name was provided in `hierarchy`')
 
-            self.set_const(name, pattern)
+            cast(MutableLibrary, self).set_const(name, pattern)
 
         return self
 
diff --git a/masque/pattern.py b/masque/pattern.py
index c557c06..09282a5 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -13,9 +13,9 @@ from numpy.typing import NDArray, ArrayLike
 # .visualize imports matplotlib and matplotlib.collections
 
 from .ref import Ref
-from .shapes import Shape
+from .shapes import Shape, Polygon
 from .label import Label
-from .utils import rotation_matrix_2d, AutoSlots, annotations_t
+from .utils import rotation_matrix_2d, annotations_t
 from .error import PatternError
 from .traits import AnnotatableImpl, Scalable, Mirrorable, Rotatable, Positionable, Repeatable
 from .ports import Port, PortList
@@ -24,7 +24,7 @@ from .ports import Port, PortList
 P = TypeVar('P', bound='Pattern')
 
 
-class Pattern(PortList, AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
+class Pattern(PortList, AnnotatableImpl, Mirrorable):
     """
     2D layout consisting of some set of shapes, labels, and references to other Pattern objects
      (via Ref). Shapes are assumed to inherit from masque.shapes.Shape or provide equivalent functions.
@@ -534,6 +534,21 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         self.refs.append(Ref(*args, **kwargs))
         return self
 
+    def rect(self: P, *args: Any, **kwargs: Any) -> P:
+        """
+        Convenience function which calls `Polygon.rect` to construct a
+         rectangle and adds it to this pattern.
+
+        Args:
+            *args: Passed to `Polygon.rect()`
+            **kwargs: Passed to `Polygon.rect()`
+
+        Returns:
+            self
+        """
+        self.shapes.append(Polygon.rect(*args, **kwargs))
+        return self
+
     def flatten(
             self: P,
             library: Mapping[str, P],
diff --git a/masque/ports.py b/masque/ports.py
index 000c866..dd73af2 100644
--- a/masque/ports.py
+++ b/masque/ports.py
@@ -11,7 +11,7 @@ from numpy import pi
 from numpy.typing import ArrayLike, NDArray
 
 from .traits import PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable
-from .utils import AutoSlots, rotate_offsets_around
+from .utils import rotate_offsets_around
 from .error import PortError
 
 
@@ -23,7 +23,7 @@ PL  = TypeVar('PL',  bound='PortList')
 PL2 = TypeVar('PL2', bound='PortList')
 
 
-class Port(PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable, metaclass=AutoSlots):
+class Port(PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable):
     """
     A point at which a `Device` can be snapped to another `Device`.
 
@@ -37,7 +37,11 @@ class Port(PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable, met
 
     The `ptype` is an arbitrary string, default of `unk` (unknown).
     """
-    __slots__ = ('ptype', '_rotation')
+    __slots__ = (
+        'ptype', '_rotation',
+        # inherited:
+        '_offset',
+        )
 
     _rotation: Optional[float]
     """ radians counterclockwise from +x, pointing into device body.
diff --git a/masque/utils/__init__.py b/masque/utils/__init__.py
index d55d9b2..4c05c49 100644
--- a/masque/utils/__init__.py
+++ b/masque/utils/__init__.py
@@ -1,7 +1,7 @@
 """
 Various helper functions, type definitions, etc.
 """
-from .types import layer_t, annotations_t
+from .types import layer_t, annotations_t, SupportsBool
 
 from .array import is_scalar
 from .autoslots import AutoSlots
diff --git a/masque/utils/types.py b/masque/utils/types.py
index 4e74306..3583726 100644
--- a/masque/utils/types.py
+++ b/masque/utils/types.py
@@ -1,8 +1,13 @@
 """
 Type definitions
 """
-from typing import Union, Tuple, Dict, List
+from typing import Union, Tuple, Dict, List, Protocol
 
 
 layer_t = Union[int, Tuple[int, int], str]
 annotations_t = Dict[str, List[Union[int, float, str]]]
+
+
+class SupportsBool(Protocol):
+    def __bool__(self) -> bool:
+        ...