@kovid, Just a follow-up...
To fix the nav-less epub3's I can use the convenient new feature of opening the TOC editor and saving which will create a new nav file, nav.html
A new line is added to the OPF manifest
Code:
<item href="nav.html" id="nav" media-type="text/html" properties="nav"/>
However, running a Check immediately afterwards shows
Code:
WARNING: The file nav.html is not referenced****[nav.html]
WARNING: The file nav.html has a mimetype that does not match its extension****[package.opf]
I'm not particularly bothered about the first WARNING but I feel a compulsion to run auto-fix to correct the second which changes the manifest item media-type to
Code:
<item href="nav.html" id="nav" media-type="application/xhtml+xml" properties="nav"/>
Is it possible to create the nav file with the correct media-type, please?