diff --git a/xarray/core/indexes.py b/xarray/core/indexes.py
index ab725f8683..987039e1f8 100644
--- a/xarray/core/indexes.py
+++ b/xarray/core/indexes.py
@@ -1476,6 +1476,9 @@ def sel(
         results = {}
         dims0 = tuple(dim_size0)
         for dim, pos in dim_positions.items():
+            # TODO: rounding the decimal positions is not always the behavior we expect
+            # (there are different ways to represent implicit intervals)
+            # we should probably make this customizable.
             pos = np.round(pos).astype("int")
             if isinstance(label0_obj, Variable):
                 xr_pos = Variable(dims0, pos)