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doc/developers/updating-modules.rst

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+
+
+Updating CMake modules
+======================
+
+To update CMake modules fetched from the web you need to run the ``update.py`` script::
+
+  cd cmake
+  python update.py ..
+
+The CMake modules are not fetched or updated at configure time or build time.
+In other words, if you never re-run ``update.py`` script and never modify the
+CMake module files, then the CMake modules will remain forever frozen.
+
+
+How to pin CMake modules to a certain version
+---------------------------------------------
+
+Sometimes you may want to avoid using the latest version of a CMake module and
+rather fetch an older version with the hash ``abcd123``. To achieve this, instead
+of::
+
+  [coverage]
+  source: https://github.com/scisoft/autocmake/raw/master/modules/code_coverage.cmake
+
+pin the version to ``abcd123`` (you do not need to specify the full Git hash, a unique
+beginning will do)::
+
+  [coverage]
+  source: https://github.com/scisoft/autocmake/raw/abcd123/modules/code_coverage.cmake