diff --git a/cuburn/code/interp.py b/cuburn/code/interp.py
index 57ee601..a2267b5 100644
--- a/cuburn/code/interp.py
+++ b/cuburn/code/interp.py
@@ -27,12 +27,7 @@ class PackerWrapper(Wrapper):
     mechanism, so you can easily nest objects by saying, for instance,
     {{pcp.camera.rotation}} from within templated code.
     """
-    def __init__(self, packer, val, spec=None, path=()):
-        super(PackerWrapper, self).__init__(val, spec)
-        self.packer, self.path = packer, path
-
-    def wrap_dict(self, path, spec, val):
-        return type(self)(self.packer, val or {}, spec, path)
+    packer = property(lambda s: s._params['packer'])
 
     def wrap_spline(self, path, spec, val):
         return PackerSpline(self.packer, path, spec)
@@ -45,7 +40,8 @@ class PackerWrapper(Wrapper):
 
     def _precalc(self):
         """Create a GenomePackerPrecalc object. See that class for details."""
-        return PrecalcWrapper(self.packer, self._val, self.spec, self.path)
+        return PrecalcWrapper(self._val, self.spec, self.path,
+                              packer=self.packer)
 
 class PackerSpline(object):
     def __init__(self, packer, path, spec):
@@ -151,7 +147,7 @@ class GenomePacker(object):
 
     def view(self, val={}):
         """Create a DataPacker view. See DataPackerView class for details."""
-        return PackerWrapper(self, val, self.spec)
+        return PackerWrapper(val, self.spec, packer=self)
 
     def _require(self, spec, path):
         """
diff --git a/cuburn/genome/use.py b/cuburn/genome/use.py
index b5ebd46..e6a2c44 100644
--- a/cuburn/genome/use.py
+++ b/cuburn/genome/use.py
@@ -10,12 +10,17 @@ class Wrapper(object):
     returned representation of the underlying genome according to the provided
     spec without imposing flow control.
     """
-    def __init__(self, val, spec=None, path=()):
+    def __init__(self, val, spec=None, path=(), **params):
+        """
+        ``**params`` are passed to any instances of this class constructed
+        during traversal. It's not used in this class but may be used by
+        deriving classes.
+        """
         if spec is None:
             assert val.get('type') in toplevels, 'Unrecognized dict type'
             spec = toplevels[val['type']]
         # plain 'val' would conflict with some variation property names
-        self._val, self.spec, self.path = val, spec, path
+        self._val, self.spec, self.path, self._params = val, spec, path, params
 
     def wrap(self, name, spec, val):
         path = self.path + (name,)
@@ -48,8 +53,9 @@ class Wrapper(object):
         return val if val is not None else spec.default
 
     def wrap_dict(self, path, spec, val):
-        return type(self)(val or {}, spec, path)
+        return type(self)(val or {}, spec, path, **self._params)
 
+    # I switched to uppercase for containers. I Don't Know Why.
     def wrap_Map(self, path, spec, val):
         return self.wrap_dict(path, spec, val)