Platform availability

Author: encukou

Doc/glossary.rst

@@ -1028,7 +1028,8 @@ Glossary
    optional module
       An :term:`extension module` that is part of the :term:`standard library`,
       but may be absent in some builds of :term:`CPython`,
-      usually due to missing third-party libraries.
+      usually due to missing third-party libraries or because the module
+      is not available for a given platform.
       See :ref:`optional-module-requirements` for a list of optional modules
       and the required libraries.