Use "impl-detail" directive where applicable.
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index d46014b..78a8a56 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -331,7 +331,7 @@
    The mathematical constant *e*.
 
 
-.. note::
+.. impl-detail::
 
    The :mod:`math` module consists mostly of thin wrappers around the platform C
    math library functions.  Behavior in exceptional cases is loosely specified