<document source="test data">
    <system_message level="3" line="1" source="test data" type="ERROR">
        <paragraph>
            Error in "sectnum" directive:
            invalid option value: (option: "start"; value: '1.2')
            invalid literal for int(): 1.2.
        <literal_block xml:space="preserve">
            .. sectnum::
               :start: 1.2