Sub-chapters in ePub file
===

The NCX file an ePub file can specify the chapters that have the book in ePub format.

It uses the following XML syntax:

    <navPoint class="chapter" id="chapter1" playOrder="1">
          <navLabel><text>Chapter 1</text></navLabel>
          <content src="file1.xhtml"/>
    </navPoint>

My question is, Can we create sub-chapters?, If so, how?.

I have searched Google and all I've found are very specific tools to perform these tasks. I do not want a tool, I want to know how to make sub-chapters in the NCX file.

Thank you,

Greetings!