title_body: Help creating a toc.ncx file for compatibility with epub 2 I have created a toc.ncx file in EPUB3 for backwards compatibility with EPUB2 . I used that file in a DRM-free book (replacing the book's toc.ncx with my own) just to see if the code was okay, but when I try to open it in Adobe Digital Editions it opens up a dialog box with the following message : 
  
  Unable to open testing.epub
  Errors were encountered in this item
  
  
  Is it not possible to test my ncx file this way? A partial code for my .ncx (just for a few headings) is below . I am creating a three-tiered list using nested navpoint tags in it. Preface is one big heading. Then there is the next big heading titled 'Heading' with Chapter 1 and 2 as its sub-headings. Chapter 2 then has its sub-sub headings with the nested navpoint tags.
  
  Could anyone please look at it and let me know if its okay?
  
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;!DOCTYPE ncx PUBLIC "-//NISO//DTD ncx 2005-1//EN" "http://www.daisy.org/z3986/2005/ncx-2005-1.dtd"&gt;
  &lt;ncx xmlns="http://www.daisy.org/z3986/2005/ncx/"  version="2005-1" xml:lang="en-US"&gt;
  &lt;head&gt;
  &lt;meta name="dtb:uid" content="uid"/&gt;
  &lt;meta name="dtb:depth" content="1"/&gt;
  &lt;meta name="dtb:totalPageCount" content="0"/&gt;
  &lt;meta name="dtb:maxPageNumber" content="0"/&gt;
  &lt;/head&gt;
  &lt;docTitle&gt;&lt;text&gt;Book Title&lt;/text&gt;&lt;/docTitle&gt;
  &lt;docAuthor&gt;&lt;text&gt;Anon, Anon&lt;/text&gt;&lt;/docAuthor&gt;
  
  
  &lt;navMap&gt;
  
          &lt;navInfo&gt;
              &lt;text&gt;THE CONTENTS&lt;/text&gt;
          &lt;/navInfo&gt;
  
          &lt;navPoint class="preface" id="preface-id" playOrder="1"&gt; 
           &lt;navLabel&gt;&lt;text&gt;Preface&lt;/text&gt;&lt;/navLabel&gt; 
           &lt;content src="" /&gt; 
          &lt;/navPoint&gt; 
  
          &lt;navPoint class="bk01" id="bk01-id" playOrder="2"&gt; 
           &lt;navLabel&gt;&lt;text&gt;Heading&lt;/text&gt;&lt;/navLabel&gt; 
           &lt;content src="" /&gt; 
                &lt;navPoint class="sect01" id="sect01-id" playOrder="3"&gt; 
                 &lt;navLabel&gt;&lt;text&gt;Chapter 1 (sub-heading of the above Heading)&lt;/text&gt;&lt;/navLabel&gt; 
                 &lt;content src="" /&gt; 
  
                &lt;/navPoint&gt; 
  
                &lt;navPoint class="sect02" id="sect02-id" playOrder="4"&gt; 
                 &lt;navLabel&gt;&lt;text&gt;Chapter 2 &lt;/text&gt;&lt;/navLabel&gt; 
                 &lt;content src="" /&gt; 
  
                     &lt;navPoint class="sect02DTL" id="sect02DTL-id" playOrder="5"&gt; 
                    &lt;navLabel&gt;&lt;text&gt;sub-heading (of chapter 2 above) &lt;/text&gt;&lt;/navLabel&gt; 
                   &lt;content src="" /&gt; 
  
                     &lt;navPoint class="sect02One" id="sect02One-id" playOrder="6"&gt; 
                    &lt;navLabel&gt;&lt;text&gt;sub-sub heading 1(is a direct link to the story text)&lt;/text&gt;&lt;/navLabel&gt; 
                   &lt;content src="" /&gt; 
                  &lt;/navPoint&gt; 
  
                  &lt;navPoint class="sect02Two" id="sect02Two-id" playOrder="7"&gt; 
                    &lt;navLabel&gt;&lt;text&gt;sub-sub heading 2&lt;/text&gt;&lt;/navLabel&gt; 
                   &lt;content src="" /&gt; 
                  &lt;/navPoint&gt;
  
                  &lt;/navPoint&gt; 
  
                &lt;/navPoint&gt; 
  
  
  
  
  
          &lt;/navPoint&gt; 
  
  
  
  &lt;/navMap&gt;
  
  &lt;/ncx&gt;
  
  
  Also, there were a few things I wanted to ask about .ncx files in general that I couldn't find sufficiently explained on the internet.
  
  
  What's the main function of the meta tags in the .ncx file ? For example the meta tags with Total Page Count and max Page Number, do they serve any role ? Could one potentially do without any of them, what would be their importance.
  I noticed a tag named PageList with nested PageTarget and navList tags in the toc.ncx file of one of the EPUB books I was looking at for reference, do these work with Kindle ?
upvoted_answer: Instead of using Adobe DE (which isn't always reliable), you should use the epubcheck validator online on your epub file. http://validator.idpf.org/
  
  You can download a copy of the validator tool on your own machine if you wish. 
  
  That will give you more verbose and  actionable error messages. 
  
  Here are some examples of error messages: https://github.com/IDPF/epubcheck/wiki/Errors (unfortunately this list doesn't seem to be complete or up to date). 
  
  My guess based on a cursory reading of your file is that there are no file references here. Here's an example from one of my own files: 
  
     &lt;navPoint id="d0e1652" playOrder="7"&gt;
              &lt;navLabel&gt;
                  &lt;text&gt;The Silver Link&lt;/text&gt;
              &lt;/navLabel&gt;
              &lt;content src="silver-link.xhtml"/&gt;
          &lt;/navPoint&gt;
          &lt;navPoint id="d0e2128" playOrder="8"&gt;
              &lt;navLabel&gt;
                  &lt;text&gt;Johnny Kinkaid&lt;/text&gt;
              &lt;/navLabel&gt;
              &lt;content src="johnny-kinkaid.xhtml"/&gt;
  
  
  But your .ncx file has an empty reference;
  
        &lt;content src="" /&gt; 
  
  
  As for your other questions, let me say that I have never had to worry about toc.ncx file problems before ... mainly because I auto-generate the file from Docbook. 
  
  The meta stuff you have is exactly what I have; IIRC, it had to do with accessibility and spoken books. 
  
  In my experience, kindlegen almost always produces a working file for kindle if you have given it a valid .epub file.