[docbook-apps] Displaying sections in TOC

[JRancier]

How can show all 'section' elements in my TOCs?  It appears that the 
default processing display two levels of nested 'section' elements, but no 
deeper.  For example:

<chapter>
    <title>Chapter displays</title>
    <section>
        <title>This section displays</title>
        <section>
            <title>This section displays</title>
            <section>
                <title>This section does NOT display</title>