Add example for option with argument choices

docsrc/options.rst

@@ -112,6 +112,22 @@ Setting argument choices
 
 The ``choices`` property can be used to specify a list of choices for an option argument in the same way as for arguments.
 
+.. code-block:: lua
+   :linenos:
+
+   parser:option "--format"
+      :choices {"short", "medium", "full"}
+
+.. code-block:: none
+
+   $ lua script.lua --format foo
+
+.. code-block:: none
+
+   Usage: script.lua [-h] [--format {short,medium,full}]
+
+   Error: argument for option '--format' must be one of 'short', 'medium', 'full'
+
 Setting number of invocations
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