diff --git a/cf_xarray/groupers.py b/cf_xarray/groupers.py
index 353d7829..8bc55ec3 100644
--- a/cf_xarray/groupers.py
+++ b/cf_xarray/groupers.py
@@ -7,6 +7,12 @@
 
 @dataclass
 class FlagGrouper(UniqueGrouper):
+    """
+    Grouper object that allows convenient categorical grouping by a CF flag variable.
+
+    Labels in the grouped output will be restricted to those listed in ``flag_meanings``.
+    """
+
     def factorize(self, group) -> EncodedGroups:
         if "flag_values" not in group.attrs or "flag_meanings" not in group.attrs:
             raise ValueError(
diff --git a/doc/api.rst b/doc/api.rst
index bc88fc86..bc3d689b 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -21,8 +21,8 @@ Geometries
 ----------
 .. autosummary::
     :toctree: generated/
-    geometry.decode_geometries
 
+    geometry.decode_geometries
     geometry.encode_geometries
     geometry.shapely_to_cf
     geometry.cf_to_shapely
@@ -33,7 +33,8 @@ Groupers
 --------
 .. autosummary::
     :toctree: generated/
-    groupers.FlagGrouper
+
+   groupers.FlagGrouper
 
 .. currentmodule:: xarray