For example...

<text>
<front> 
<!-- titlepage, etc here -->
</front>
<body>
<div type='book' n='I' xml:id='JA0100'>
<head>Book I.</head>
<div type='chapter' n='1' xml:id='JA0101'>
<head>Of writing lives in general,...
<!-- remainder of chapter 1 here -->
</div>
<div n='2' xml:id='JA0102'>
<!-- chapter 2 here -->
</div>
<!-- remainder of book 1 here -->
</div>
<div type='book' n='II' xml:id='JA0200'>
<!-- book 2 here -->
</div>
<!-- remaining books here -->
</body></text>