There must be more to it… After all, the DOCTYPE is just a minor detail; there must be something worse going on.
And what does the "Well-Formed Check EPUB" (F7) say?
Please try another test:
- Take your already-processed file, with the DOCTYPE and everything else perfect.
- Run "Mend and Prettify."
- Does it work? OK, let's move on.
- In one of the XHTML files, remove the DOCTYPE.
- Run "Mend and Prettify."
- Does it work? It does for me.
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I don’t want to make life difficult for anyone or change the habits users have developed over the years while working with Sigil.
For me, this extra safeguard is useful, and even if it’s removed, I can still add it to my build.