diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a6236e261d..ed4959bf82 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -333,12 +333,12 @@ jobs:
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[ci skip]')"
     strategy:
       matrix:
-        os: [ubuntu-16.04, windows-2016, macOS-latest]
+        os: [ubuntu-18.04, windows-2016, macOS-latest]
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v1
     - name: Install dependencies (Ubuntu)
-      if: matrix.os == 'ubuntu-16.04'
+      if: matrix.os == 'ubuntu-18.04'
       run: |
         sudo apt-get update
         sudo apt-get install build-essential bison flex libfreetype6-dev libgl1-mesa-dev libjpeg-dev libode-dev libopenal-dev libpng-dev libssl-dev libvorbis-dev libx11-dev libxcursor-dev libxrandr-dev nvidia-cg-toolkit zlib1g-dev
diff --git a/direct/src/interval/MetaInterval.py b/direct/src/interval/MetaInterval.py
index 2986071ba4..f706c338aa 100644
--- a/direct/src/interval/MetaInterval.py
+++ b/direct/src/interval/MetaInterval.py
@@ -348,10 +348,14 @@ class MetaInterval(CMetaInterval):
     def getManager(self):
         return self.__manager
 
+    manager = property(getManager, setManager)
+
     def setT(self, t):
         self.__updateIvals()
         CMetaInterval.setT(self, t)
 
+    t = property(CMetaInterval.getT, setT)
+
     def start(self, startT = 0.0, endT = -1.0, playRate = 1.0):
         self.__updateIvals()
         self.setupPlay(startT, endT, playRate, 0)
@@ -475,6 +479,8 @@ class MetaInterval(CMetaInterval):
         else:
             CMetaInterval.setPlayRate(self, playRate)
 
+    play_rate = property(CMetaInterval.getPlayRate, setPlayRate)
+
     def __doPythonCallbacks(self):
         # This function invokes any Python-level Intervals that need
         # to be invoked at this point in time.  It must be called
@@ -549,6 +555,8 @@ class MetaInterval(CMetaInterval):
         self.__updateIvals()
         return CMetaInterval.getDuration(self)
 
+    duration = property(getDuration)
+
     def __repr__(self, *args, **kw):
         # This function overrides from the parent level to force it to
         # update the interval list first, if necessary.
diff --git a/direct/src/showbase/ShowBase.py b/direct/src/showbase/ShowBase.py
index 53c30a3e9c..c7edea715e 100644
--- a/direct/src/showbase/ShowBase.py
+++ b/direct/src/showbase/ShowBase.py
@@ -725,7 +725,7 @@ class ShowBase(DirectObject.DirectObject):
                               of :meth:`~panda3d.core.GraphicsWindow.setUnexposedDraw()`.
 
         :param callbackWindowDict: If not None, a
-                                   :class:`~panda3d.core.CallbackGraphicWindow`
+                                   :class:`~panda3d.core.CallbackGraphicsWindow`
                                    is created instead, which allows the caller
                                    to create the actual window with its own
                                    OpenGL context, and direct Panda's rendering
diff --git a/makepanda/installer.nsi b/makepanda/installer.nsi
index 672ae4d37e..bf4b2013be 100644
--- a/makepanda/installer.nsi
+++ b/makepanda/installer.nsi
@@ -374,6 +374,7 @@ SectionGroup "Python modules" SecGroupPython
         !insertmacro PyBindingSection 3.8-32 .cp38-win32.pyd
         !insertmacro PyBindingSection 3.9-32 .cp39-win32.pyd
         !insertmacro PyBindingSection 3.10-32 .cp310-win32.pyd
+        !insertmacro PyBindingSection 3.11-32 .cp311-win32.pyd
     !else
         !insertmacro PyBindingSection 3.5 .cp35-win_amd64.pyd
         !insertmacro PyBindingSection 3.6 .cp36-win_amd64.pyd
@@ -381,6 +382,7 @@ SectionGroup "Python modules" SecGroupPython
         !insertmacro PyBindingSection 3.8 .cp38-win_amd64.pyd
         !insertmacro PyBindingSection 3.9 .cp39-win_amd64.pyd
         !insertmacro PyBindingSection 3.10 .cp310-win_amd64.pyd
+        !insertmacro PyBindingSection 3.11 .cp311-win_amd64.pyd
     !endif
 SectionGroupEnd
 
@@ -489,6 +491,7 @@ Function .onInit
         ${If} ${AtLeastWin8}
         !insertmacro MaybeEnablePyBindingSection 3.9-32
         !insertmacro MaybeEnablePyBindingSection 3.10-32
+        !insertmacro MaybeEnablePyBindingSection 3.11-32
         ${EndIf}
     !else
         !insertmacro MaybeEnablePyBindingSection 3.5
@@ -498,6 +501,7 @@ Function .onInit
         ${If} ${AtLeastWin8}
         !insertmacro MaybeEnablePyBindingSection 3.9
         !insertmacro MaybeEnablePyBindingSection 3.10
+        !insertmacro MaybeEnablePyBindingSection 3.11
         ${EndIf}
     !endif
 
@@ -511,6 +515,10 @@ Function .onInit
         SectionSetFlags ${SecPyBindings3.10} ${SF_RO}
         SectionSetInstTypes ${SecPyBindings3.10} 0
     !endif
+    !ifdef SecPyBindings3.11
+        SectionSetFlags ${SecPyBindings3.11} ${SF_RO}
+        SectionSetInstTypes ${SecPyBindings3.11} 0
+    !endif
     ${EndUnless}
 FunctionEnd
 
@@ -822,6 +830,7 @@ Section Uninstall
         !insertmacro RemovePythonPath 3.8-32
         !insertmacro RemovePythonPath 3.9-32
         !insertmacro RemovePythonPath 3.10-32
+        !insertmacro RemovePythonPath 3.11-32
     !else
         !insertmacro RemovePythonPath 3.5
         !insertmacro RemovePythonPath 3.6
@@ -829,6 +838,7 @@ Section Uninstall
         !insertmacro RemovePythonPath 3.8
         !insertmacro RemovePythonPath 3.9
         !insertmacro RemovePythonPath 3.10
+        !insertmacro RemovePythonPath 3.11
     !endif
 
     SetDetailsPrint both
@@ -897,6 +907,7 @@ SectionEnd
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.8-32} $(DESC_SecPyBindings3.8-32)
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.9-32} $(DESC_SecPyBindings3.9-32)
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.10-32} $(DESC_SecPyBindings3.10-32)
+    !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.11-32} $(DESC_SecPyBindings3.11-32)
   !else
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.5} $(DESC_SecPyBindings3.5)
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.6} $(DESC_SecPyBindings3.6)
@@ -904,6 +915,7 @@ SectionEnd
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.8} $(DESC_SecPyBindings3.8)
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.9} $(DESC_SecPyBindings3.9)
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.10} $(DESC_SecPyBindings3.10)
+    !insertmacro MUI_DESCRIPTION_TEXT ${SecPyBindings3.11} $(DESC_SecPyBindings3.11)
   !endif
   !ifdef INCLUDE_PYVER
     !insertmacro MUI_DESCRIPTION_TEXT ${SecPython} $(DESC_SecPython)
diff --git a/panda/src/bullet/bulletDebugNode.I b/panda/src/bullet/bulletDebugNode.I
index eae681aba5..e29863669f 100644
--- a/panda/src/bullet/bulletDebugNode.I
+++ b/panda/src/bullet/bulletDebugNode.I
@@ -20,7 +20,7 @@ INLINE BulletDebugNode::
 }
 
 /**
- *
+ * If true, displays collision shapes in wireframe mode.
  */
 INLINE void BulletDebugNode::
 show_wireframe(bool show) {
@@ -39,7 +39,8 @@ get_show_wireframe() const {
 }
 
 /**
- *
+ * If true, display limits defined for constraints, e.g. a pivot axis or maximum
+ * amplitude.
  */
 INLINE void BulletDebugNode::
 show_constraints(bool show) {
@@ -58,7 +59,7 @@ get_show_constraints() const {
 }
 
 /**
- *
+ * If true, displays axis aligned bounding boxes for objects.
  */
 INLINE void BulletDebugNode::
 show_bounding_boxes(bool show) {
@@ -77,7 +78,7 @@ get_show_bounding_boxes() const {
 }
 
 /**
- *
+ * If true, displays normal vectors for triangle mesh and heightfield faces.
  */
 INLINE void BulletDebugNode::
 show_normals(bool show) {
@@ -92,4 +93,4 @@ INLINE bool BulletDebugNode::
 get_show_normals() const {
 
   return _drawer._normals;
-}
\ No newline at end of file
+}
diff --git a/panda/src/bullet/bulletPersistentManifold.cxx b/panda/src/bullet/bulletPersistentManifold.cxx
index 9876ff35ee..f5e96d0464 100644
--- a/panda/src/bullet/bulletPersistentManifold.cxx
+++ b/panda/src/bullet/bulletPersistentManifold.cxx
@@ -49,6 +49,8 @@ get_contact_processing_threshold() const {
  */
 void BulletPersistentManifold::
 clear_manifold() {
+  nassertv_always(_manifold != nullptr);
+
   LightMutexHolder holder(BulletWorld::get_global_lock());
 
   _manifold->clearManifold();
@@ -59,6 +61,8 @@ clear_manifold() {
  */
 PandaNode *BulletPersistentManifold::
 get_node0() {
+  nassertr_always(_manifold != nullptr, nullptr);
+
   LightMutexHolder holder(BulletWorld::get_global_lock());
 
 #if BT_BULLET_VERSION >= 281
@@ -75,6 +79,8 @@ get_node0() {
  */
 PandaNode *BulletPersistentManifold::
 get_node1() {
+  nassertr_always(_manifold != nullptr, nullptr);
+
   LightMutexHolder holder(BulletWorld::get_global_lock());
 
 #if BT_BULLET_VERSION >= 281
@@ -91,6 +97,8 @@ get_node1() {
  */
 int BulletPersistentManifold::
 get_num_manifold_points() const {
+  nassertr_always(_manifold != nullptr, 0);
+
   LightMutexHolder holder(BulletWorld::get_global_lock());
 
   return _manifold->getNumContacts();
@@ -107,3 +115,12 @@ get_manifold_point(int idx) const {
 
   return new BulletManifoldPoint(_manifold->getContactPoint(idx));
 }
+
+/**
+ *
+ */
+BulletManifoldPoint BulletPersistentManifold::
+__get_manifold_point(int idx) const {
+  LightMutexHolder holder(BulletWorld::get_global_lock());
+  return BulletManifoldPoint(_manifold->getContactPoint(idx));
+}
diff --git a/panda/src/bullet/bulletPersistentManifold.h b/panda/src/bullet/bulletPersistentManifold.h
index 0b994c6bac..06e9b47564 100644
--- a/panda/src/bullet/bulletPersistentManifold.h
+++ b/panda/src/bullet/bulletPersistentManifold.h
@@ -35,7 +35,8 @@ PUBLISHED:
 
   int get_num_manifold_points() const;
   BulletManifoldPoint *get_manifold_point(int idx) const;
-  MAKE_SEQ(get_manifold_points, get_num_manifold_points, get_manifold_point);
+  BulletManifoldPoint __get_manifold_point(int idx) const;
+  MAKE_SEQ(get_manifold_points, get_num_manifold_points, __get_manifold_point);
 
   PN_stdfloat get_contact_breaking_threshold() const;
   PN_stdfloat get_contact_processing_threshold() const;
@@ -44,7 +45,7 @@ PUBLISHED:
 
   MAKE_PROPERTY(node0, get_node0);
   MAKE_PROPERTY(node1, get_node1);
-  MAKE_SEQ_PROPERTY(manifold_points, get_num_manifold_points, get_manifold_point);
+  MAKE_SEQ_PROPERTY(manifold_points, get_num_manifold_points, __get_manifold_point);
   MAKE_PROPERTY(contact_breaking_threshold, get_contact_breaking_threshold);
   MAKE_PROPERTY(contact_processing_threshold, get_contact_processing_threshold);
 
diff --git a/panda/src/bullet/bulletWorld.cxx b/panda/src/bullet/bulletWorld.cxx
index a76b0e8007..4874f86db3 100644
--- a/panda/src/bullet/bulletWorld.cxx
+++ b/panda/src/bullet/bulletWorld.cxx
@@ -1074,6 +1074,19 @@ get_manifold(int idx) const {
   return (ptr) ? new BulletPersistentManifold(ptr) : nullptr;
 }
 
+/**
+ *
+ */
+BulletPersistentManifold BulletWorld::
+__get_manifold(int idx) const {
+  LightMutexHolder holder(get_global_lock());
+
+  nassertr(idx < _dispatcher->getNumManifolds(), BulletPersistentManifold(nullptr));
+
+  btPersistentManifold *ptr = _dispatcher->getManifoldByIndexInternal(idx);
+  return BulletPersistentManifold(ptr);
+}
+
 /**
  *
  */
diff --git a/panda/src/bullet/bulletWorld.h b/panda/src/bullet/bulletWorld.h
index b655e0b349..669c8944d3 100644
--- a/panda/src/bullet/bulletWorld.h
+++ b/panda/src/bullet/bulletWorld.h
@@ -128,7 +128,8 @@ PUBLISHED:
   // Manifolds
   int get_num_manifolds() const;
   BulletPersistentManifold *get_manifold(int idx) const;
-  MAKE_SEQ(get_manifolds, get_num_manifolds, get_manifold);
+  BulletPersistentManifold __get_manifold(int idx) const;
+  MAKE_SEQ(get_manifolds, get_num_manifolds, __get_manifold);
 
   // Collision filtering
   void set_group_collision_flag(unsigned int group1, unsigned int group2, bool enable);
@@ -168,7 +169,7 @@ PUBLISHED:
   MAKE_SEQ_PROPERTY(characters, get_num_characters, get_character);
   MAKE_SEQ_PROPERTY(vehicles, get_num_vehicles, get_vehicle);
   MAKE_SEQ_PROPERTY(constraints, get_num_constraints, get_constraint);
-  MAKE_SEQ_PROPERTY(manifolds, get_num_manifolds, get_manifold);
+  MAKE_SEQ_PROPERTY(manifolds, get_num_manifolds, __get_manifold);
   MAKE_PROPERTY(force_update_all_aabbs, get_force_update_all_aabbs,
                                         set_force_update_all_aabbs);
 
diff --git a/panda/src/pgraph/planeNode.h b/panda/src/pgraph/planeNode.h
index 2b58225abd..6debd7a217 100644
--- a/panda/src/pgraph/planeNode.h
+++ b/panda/src/pgraph/planeNode.h
@@ -65,6 +65,11 @@ PUBLISHED:
   INLINE void set_clip_effect(int clip_effect);
   INLINE int get_clip_effect() const;
 
+  MAKE_PROPERTY(plane, get_plane, set_plane);
+  MAKE_PROPERTY(viz_scale, get_viz_scale, set_viz_scale);
+  MAKE_PROPERTY(priority, get_priority, set_priority);
+  MAKE_PROPERTY(clip_effect, get_clip_effect, set_clip_effect);
+
 public:
   INLINE static UpdateSeq get_sort_seq();