<document source="test data">
    <system_message level="1" line="1" source="test data" type="INFO">
        <paragraph>
            Possible incomplete section title.
            Treating the overline as ordinary text because it's so short.
    <section dupnames="..." ids="id1">
        <title>
            ...
        <system_message level="1" line="4" source="test data" type="INFO">
            <paragraph>
                Possible incomplete section title.
                Treating the overline as ordinary text because it's so short.
        <section dupnames="..." ids="id2">
            <title>
                ...
            <system_message backrefs="id2" level="1" line="5" source="test data" type="INFO">
                <paragraph>
                    Duplicate implicit target name: "...".
            <section dupnames="..." ids="id3">
                <title>
                    ...
                <system_message backrefs="id3" level="1" line="8" source="test data" type="INFO">
                    <paragraph>
                        Duplicate implicit target name: "...".