Displaying sections in TOC

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>