diff --git a/docs/source/io_formats/nuclear_data.rst b/docs/source/io_formats/nuclear_data.rst
index ef61604cb..8174108e1 100644
--- a/docs/source/io_formats/nuclear_data.rst
+++ b/docs/source/io_formats/nuclear_data.rst
@@ -339,6 +339,16 @@ Incoherent elastic scattering
               [eV\ :math:`^{-1}`].
 :Attributes: - **type** (*char[]*) -- 'IncoherentElastic'
 
+Sum of functions
+----------------
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "Sum"
+             - **n** (*int*) -- Number of functions
+:Datasets:
+           - ***func_<i>** (:ref:`function <1d_functions>`) -- Dataset for the
+             i-th function (indexing starts at 1)
+
 .. _angle_energy:
 
 --------------------------
@@ -501,6 +511,19 @@ equiprobable bins.
            - **skewed** (*int8_t*) -- Whether discrete angles are equi-probable
              (0) or have a skewed distribution (1).
 
+Mixed Elastic
+-------------
+
+This angle-energy distribution is used when an evaluation specifies both
+coherent and incoherent elastic thermal neutron scattering.
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "mixed_elastic"
+:Groups: - **coherent** -- Distribution for coherent elastic scattering. The
+           format is given in :ref:`angle_energy`.
+         - **incoherent** -- Distribution for incoherent elastic scattering.
+           The format is given in :ref:`angle_energy`.
+
 .. _energy_distribution:
 
 --------------------
diff --git a/docs/source/pythonapi/data.rst b/docs/source/pythonapi/data.rst
index 287738774..c74769be6 100644
--- a/docs/source/pythonapi/data.rst
+++ b/docs/source/pythonapi/data.rst
@@ -116,6 +116,7 @@ Angle-Energy Distributions
     IncoherentElasticAE
     IncoherentElasticAEDiscrete
     IncoherentInelasticAEDiscrete
+    MixedElasticAE
 
 Resonance Data
 --------------
diff --git a/openmc/data/function.py b/openmc/data/function.py
index 7a73987df..751f6cdb5 100644
--- a/openmc/data/function.py
+++ b/openmc/data/function.py
@@ -581,6 +581,8 @@ class Sum(EqualityMixin):
     def to_hdf5(self, group, name='xy'):
         """Write sum of functions to an HDF5 group
 
+        .. versionadded:: 0.13.1
+
         Parameters
         ----------
         group : h5py.Group
@@ -599,6 +601,8 @@ class Sum(EqualityMixin):
     def from_hdf5(cls, group):
         """Generate sum of functions from an HDF5 group
 
+        .. versionadded:: 0.13.1
+
         Parameters
         ----------
         group : h5py.Group
diff --git a/openmc/data/thermal_angle_energy.py b/openmc/data/thermal_angle_energy.py
index d7dfe92f9..b7ca349f1 100644
--- a/openmc/data/thermal_angle_energy.py
+++ b/openmc/data/thermal_angle_energy.py
@@ -36,6 +36,9 @@ class CoherentElasticAE(AngleEnergy):
     def to_hdf5(self, group, xs_group=None):
         """Write coherent elastic distribution to an HDF5 group
 
+        .. versionchanged:: 0.13.1
+            The *xs_group* argument was added.
+
         Parameters
         ----------
         group : h5py.Group
@@ -220,6 +223,8 @@ class IncoherentInelasticAE(CorrelatedAngleEnergy):
 class MixedElasticAE(AngleEnergy):
     """Secondary distribution for mixed coherent/incoherent thermal elastic
 
+    .. versionadded:: 0.13.1
+
     Parameters
     ----------
     coherent : AngleEnergy