Hi PKTC:
To make the automated Sigil rename functionality clear since the approach is not always obvious:
In Sigil's BookBrowser:
1. highlight all of your .htm (or .html) files at the same time.
2. Right mouse click to raise the context menu and select Rename
3. In the "Rename Files Starting At:" dialog box that comes up, remove anything there and enter just ".xhtml" (no quotes). Then it "OK"
All of your files will be automatically renamed to .xhtml files (with no other name changes) and all of the internal links and references will be properly updated.
Hope this helps,
KevinH
ps. To document this requirement, I added these instructions to the ePub3-itizer main thread:
https://www.mobileread.com/forums/sho...d.php?t=250566