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+Periodic Taskgraphs
+===================
+
+The cron functionality allows in-tree scheduling of task graphs that run
+periodically, instead of on a push.
+
+
+Cron.yml
+--------
+
+In the root of the Comm directory, you will find `.cron.yml`.  This defines
+the periodic tasks ("cron jobs") that run for Thunderbird.
+
+See `the Firefox CI cron documentation <https://firefox-source-docs.mozilla.org/taskcluster/cron.html>`_
+for a description of `.cron.yml`.
+
+
+Disabling Cron Jobs
+-------------------
+
+Sometimes due to build bustage, it's desirable to disable the automatic
+Thunderbird Daily builds. The best way to do this is to change `.cron.yml`
+so that the jobs are never scheduled. This is done by changing `when` to an
+empty list.
+
+The Daily build is started by the `nightly-desktop` job. Additionally, there
+is a `searchfox-index` job that should be disabled as well when disabling
+Dailies.
+
+For both of these, comment out the `when` line that sets a time and uncomment
+the next line which sets an empty list.
+
+.. code-block:: yaml
+  :linenos:
+  :emphasize-lines: 8,9
+
+    - name: nightly-desktop
+      job:
+          type: decision-task
+          treeherder-symbol: Nd
+          target-tasks-method: nightly_desktop
+      run-on-projects:
+          - comm-central
+      when: [{hour: 11, minute: 0}]
+      # when: []
+
+
+L10n-bump Cron Job
+------------------
+
+`l10n-bump` runs daily on comm-beta. For RC week (week 4) it needs to be
+disabled by pushing a change directly to `comm-beta` setting ``when`` to
+an empty list as above.
+
+**Do not make the change on comm-central first.** `l10n-bump` will be
+re-enabled by merge day activities automatically.