I have been getting the well-formed error message on epub 3 ebooks after I specifically Add Semantic...[mark Cover]. This adds the following to nav.xhtml:
Code:
<nav epub:type="landmarks" id="landmarks" hidden="">
<h1>Landmarks</h1>
<ol>
<li>
<a epub:type="cover" href="cover.xhtml">Cover</a>
</li>
</ol>
</nav>
Thereafter anytime I make a change and hit Save, I will get the well-formed error message. Clicking Yes makes the dialog go away but it reappears again at the next save.
Removing the offending section causes the error message to NOT reappear.
--MH