diff --git a/armi/reactor/blueprints/isotopicOptions.py b/armi/reactor/blueprints/isotopicOptions.py
index ead85253f..f39f5c9ea 100644
--- a/armi/reactor/blueprints/isotopicOptions.py
+++ b/armi/reactor/blueprints/isotopicOptions.py
@@ -150,6 +150,10 @@ class CustomIsotopic(yamlize.Map):
     """
     User specified, custom isotopics input defined by a name (such as MOX), and key/pairs of nuclide names and numeric
     values consistent with the ``input format``.
+
+    .. impl:: Certain material modifications will be applied using this code.
+        :id: I_ARMI_MAT_USER_INPUT2
+        :implements: R_ARMI_MAT_USER_INPUT
     """
 
     key_type = yamlize.Typed(str)