diff --git a/.github/workflows/ci-pre-commit-autoupdate.yaml b/.github/workflows/ci-pre-commit-autoupdate.yaml
deleted file mode 100644
index b10a541197e..00000000000
--- a/.github/workflows/ci-pre-commit-autoupdate.yaml
+++ /dev/null
@@ -1,44 +0,0 @@
-name: "pre-commit autoupdate CI"
-
-on:
-  schedule:
-    - cron: "0 0 * * 0"  # every Sunday at 00:00 UTC
-  workflow_dispatch:
-
-
-jobs:
-  autoupdate:
-    name: 'pre-commit autoupdate'
-    runs-on: ubuntu-latest
-    if: github.repository == 'pydata/xarray'
-    steps:
-      - name: checkout
-        uses: actions/checkout@v2
-      - name: Cache pip and pre-commit
-        uses: actions/cache@v2
-        with:
-          path: |
-            ~/.cache/pre-commit
-            ~/.cache/pip
-          key: ${{ runner.os }}-pre-commit-autoupdate
-      - name: setup python
-        uses: actions/setup-python@v2
-      - name: upgrade pip
-        run: python -m pip install --upgrade pip
-      - name: install dependencies
-        run: python -m pip install --upgrade pre-commit pyyaml packaging
-      - name: version info
-        run: python -m pip list
-      - name: autoupdate
-        uses: technote-space/create-pr-action@837dbe469b39f08d416889369a52e2a993625c84
-        with:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          EXECUTE_COMMANDS: |
-            python -m pre_commit autoupdate
-            python -m pre_commit run --all-files
-          COMMIT_MESSAGE: 'pre-commit: autoupdate hook versions'
-          COMMIT_NAME: 'github-actions[bot]'
-          COMMIT_EMAIL: 'github-actions[bot]@users.noreply.github.com'
-          PR_TITLE: 'pre-commit: autoupdate hook versions'
-          PR_BRANCH_PREFIX: 'pre-commit/'
-          PR_BRANCH_NAME: 'autoupdate-${PR_ID}'
diff --git a/CITATION.cff b/CITATION.cff
new file mode 100644
index 00000000000..fcc04a6f3e4
--- /dev/null
+++ b/CITATION.cff
@@ -0,0 +1,96 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+- family-names: "Hoyer"
+  given-names: "Stephan"
+  orcid: "https://orcid.org/0000-0002-5207-0380"
+- family-names: "Roos"
+  given-names: "Maximilian"
+- family-names: "Joseph"
+  given-names: "Hamman"
+  orcid: "https://orcid.org/0000-0001-7479-8439"
+- family-names: "Magin"
+  given-names: "Justus"
+- family-names: "Cherian"
+  given-names: "Deepak"
+  orcid: "https://orcid.org/0000-0002-6861-8734"
+- family-names: "Fitzgerald"
+  given-names: "Clark"
+  orcid: "https://orcid.org/0000-0003-3446-6389"
+- family-names: "Hauser"
+  given-names: "Mathias"
+  orcid: "https://orcid.org/0000-0002-0057-4878"
+- family-names: "Fujii"
+  given-names: "Keisuke"
+  orcid: "https://orcid.org/0000-0003-0390-9984"
+- family-names: "Maussion"
+  given-names: "Fabien"
+  orcid: "https://orcid.org/0000-0002-3211-506X"
+- family-names: "Imperiale"
+  given-names: "Guido"
+- family-names: "Clark"
+  given-names: "Spencer"
+  orcid: "https://orcid.org/0000-0001-5595-7895"
+- family-names: "Kleeman"
+  given-names: "Alex"
+- family-names: "Nicholas"
+  given-names: "Thomas"
+  orcid: "https://orcid.org/0000-0002-2176-0530"
+- family-names: "Kluyver"
+  given-names: "Thomas"
+  orcid: "https://orcid.org/0000-0003-4020-6364"
+- family-names: "Westling"
+  given-names: "Jimmy"
+- family-names: "Munroe"
+  given-names: "James"
+  orcid: "https://orcid.org/0000-0001-9098-6309"
+- family-names: "Amici"
+  given-names: "Alessandro"
+  orcid: "https://orcid.org/0000-0002-1778-4505"
+- family-names: "Barghini"
+  given-names: "Aureliana"
+- family-names: "Banihirwe"
+  given-names: "Anderson"
+  orcid: "https://orcid.org/0000-0001-6583-571X"
+- family-names: "Bell"
+  given-names: "Ray"
+  orcid: "https://orcid.org/0000-0003-2623-0587"
+- family-names: "Hatfield-Dodds"
+  given-names: "Zac"
+  orcid: "https://orcid.org/0000-0002-8646-8362"
+- family-names: "Abernathey"
+  given-names: "Ryan"
+  orcid: "https://orcid.org/0000-0001-5999-4917"
+- family-names: "Bovy"
+  given-names: "Benoît"
+- family-names: "Omotani"
+  given-names: "John"
+  orcid: "https://orcid.org/0000-0002-3156-8227"
+- family-names: "Mühlbauer"
+  given-names: "Kai"
+  orcid: "https://orcid.org/0000-0001-6599-1034"
+- family-names: "Roszko"
+  given-names: "Maximilian K."
+  orcid: "https://orcid.org/0000-0001-9424-2526"
+- family-names: "Wolfram"
+  given-names: "Phillip J."
+  orcid: "https://orcid.org/0000-0001-5971-4241"
+title: "xarray"
+doi: 10.5281/zenodo.598201
+url: "https://github.com/pydata/xarray"
+preferred-citation:
+  type: article
+  authors:
+  - family-names: "Hoyer"
+    given-names: "Stephan"
+    orcid: "https://orcid.org/0000-0002-5207-0380"
+  - family-names: "Joseph"
+    given-names: "Hamman"
+    orcid: "https://orcid.org/0000-0001-7479-8439"
+  doi: "10.5334/jors.148"
+  journal: "Journal of Open Research Software"
+  month: 4
+  title: "xarray: N-D labeled Arrays and Datasets in Python"
+  volume: 5
+  issue: 1
+  year: 2017
diff --git a/xarray/backends/plugins.py b/xarray/backends/plugins.py
index bcaee498b90..32013f1f298 100644
--- a/xarray/backends/plugins.py
+++ b/xarray/backends/plugins.py
@@ -1,15 +1,16 @@
 import functools
 import inspect
 import itertools
+import sys
 import warnings
 
 from .common import BACKEND_ENTRYPOINTS, BackendEntrypoint
 
-try:
+if sys.version_info >= (3, 8):
     from importlib.metadata import entry_points
-except ImportError:
+else:
     # if the fallback library is missing, we are doomed.
-    from importlib_metadata import entry_points  # type: ignore[no-redef]
+    from importlib_metadata import entry_points
 
 
 STANDARD_BACKENDS_ORDER = ["netcdf4", "h5netcdf", "scipy"]
diff --git a/xarray/core/dataarray.py b/xarray/core/dataarray.py
index 89f916db7f4..24e5f5736b0 100644
--- a/xarray/core/dataarray.py
+++ b/xarray/core/dataarray.py
@@ -2726,9 +2726,11 @@ def to_dataframe(
         """Convert this array and its coordinates into a tidy pandas.DataFrame.
 
         The DataFrame is indexed by the Cartesian product of index coordinates
-        (in the form of a :py:class:`pandas.MultiIndex`).
+        (in the form of a :py:class:`pandas.MultiIndex`). Other coordinates are
+        included as columns in the DataFrame.
 
-        Other coordinates are included as columns in the DataFrame.
+        For 1D and 2D DataArrays, see also :py:func:`DataArray.to_pandas` which
+        doesn't rely on a MultiIndex to build the DataFrame.
 
         Parameters
         ----------
@@ -2750,6 +2752,9 @@ def to_dataframe(
         result
             DataArray as a pandas DataFrame.
 
+        See also
+        --------
+        DataArray.to_pandas
         """
         if name is None:
             name = self.name
diff --git a/xarray/core/formatting_html.py b/xarray/core/formatting_html.py
index faad06d8093..072a932b943 100644
--- a/xarray/core/formatting_html.py
+++ b/xarray/core/formatting_html.py
@@ -255,7 +255,7 @@ def _obj_repr(obj, header_components, sections):
         "<div>"
         f"{icons_svg}<style>{css_style}</style>"
         f"<pre class='xr-text-repr-fallback'>{escape(repr(obj))}</pre>"
-        "<div class='xr-wrap' hidden>"
+        "<div class='xr-wrap' style='display:none'>"
         f"{header}"
         f"<ul class='xr-sections'>{sections}</ul>"
         "</div>"
diff --git a/xarray/core/variable.py b/xarray/core/variable.py
index a96adb31e64..52125ec4113 100644
--- a/xarray/core/variable.py
+++ b/xarray/core/variable.py
@@ -2813,6 +2813,11 @@ def name(self):
     def name(self, value):
         raise AttributeError("cannot modify name of IndexVariable in-place")
 
+    def _inplace_binary_op(self, other, f):
+        raise TypeError(
+            "Values of an IndexVariable are immutable and can not be modified inplace"
+        )
+
 
 # for backwards compatibility
 Coordinate = utils.alias(IndexVariable, "Coordinate")
diff --git a/xarray/static/css/style.css b/xarray/static/css/style.css
index 373624b8a9d..b3b8a162e9a 100644
--- a/xarray/static/css/style.css
+++ b/xarray/static/css/style.css
@@ -26,7 +26,7 @@ body.vscode-dark {
 }
 
 .xr-wrap {
-  display: block;
+  display: block !important;
   min-width: 300px;
   max-width: 700px;
 }
diff --git a/xarray/tests/test_dataarray.py b/xarray/tests/test_dataarray.py
index 53c650046e7..5e9c1b87ce2 100644
--- a/xarray/tests/test_dataarray.py
+++ b/xarray/tests/test_dataarray.py
@@ -1987,6 +1987,18 @@ def test_inplace_math_basics(self):
         assert_array_equal(b.values, x)
         assert source_ndarray(b.values) is x
 
+    def test_inplace_math_error(self):
+        data = np.random.rand(4)
+        times = np.arange(4)
+        foo = DataArray(data, coords=[times], dims=["time"])
+        b = times.copy()
+        with pytest.raises(
+            TypeError, match=r"Values of an IndexVariable are immutable"
+        ):
+            foo.coords["time"] += 1
+        # Check error throwing prevented inplace operation
+        assert_array_equal(foo.coords["time"], b)
+
     def test_inplace_math_automatic_alignment(self):
         a = DataArray(range(5), [("x", range(5))])
         b = DataArray(range(1, 6), [("x", range(1, 6))])
diff --git a/xarray/tests/test_variable.py b/xarray/tests/test_variable.py
index 9c0e45c5da9..3267af8b45b 100644
--- a/xarray/tests/test_variable.py
+++ b/xarray/tests/test_variable.py
@@ -1656,6 +1656,14 @@ def test_inplace_math(self):
         with pytest.raises(ValueError, match=r"dimensions cannot change"):
             v += Variable("y", np.arange(5))
 
+    def test_inplace_math_error(self):
+        x = np.arange(5)
+        v = IndexVariable(["x"], x)
+        with pytest.raises(
+            TypeError, match=r"Values of an IndexVariable are immutable"
+        ):
+            v += 1
+
     def test_reduce(self):
         v = Variable(["x", "y"], self.d, {"ignored": "attributes"})
         assert_identical(v.reduce(np.std, "x"), Variable(["y"], self.d.std(axis=0)))