<document source="test data">
    <section ids="main-title" names="main title">
        <title>
            Main title
        <section ids="subtitle-1" names="subtitle 1">
            <title>
                Subtitle 1
            <section ids="sub-subtitle" names="sub-subtitle">
                <title>
                    Sub-subtitle
    <section ids="another-main-title" names="another main title">
        <title>
            Another main title
        <system_message level="3" line="15" source="test data" type="ERROR">
            <paragraph>
                Title level inconsistent:
            <literal_block xml:space="preserve">
                ~~~~~~~~~~~~~~~~~~
                Inconsistent title
                ~~~~~~~~~~~~~~~~~~
        <section ids="inconsistent-title" names="inconsistent title">
            <title>
                Inconsistent title