Wow. More adventuring.
I sent a message to a friend asking for their address so I could send them a copy of the Toki Pona translation of TLLF. And we ended up having a long discussion.
I sent along copies of the PDF and the epub of the book, and… the epub did not open properly in the Sumatra PDF/epub reader on Windows!
A screenshot revealed that Sumatra was attempting to display the ebook as if it were a reflowable ebook (thanks to Anne-Marie Concepción’s epub course on LinkedIn Learning, I know what that looks like). Plus, it wasn’t displaying the sitelen pona font at all.
So during the discussion, I fired up my Windows 10 virtual machine for the first time in quite a while (I run an Intel Mac), installed Sumatra PDF, and opened the epub. And the same error happened.
Afterwards, more experimentation. So far I have established:
Sumatra PDF/epub viewer (Windows only) does not seem to have any idea that fixed-format ebooks exist. There is no mention of them in the program’s documentation or settings. It tries to display the epub as a reflowable-format epub.
Adobe Digital Editions displays the epub properly on MacOS 10.15 but not on Windows 10. On Windows, it positions most of the text properly, but the sitelen pona font is not shown at all, and the text that would have that font applied is shown overlapping the latin-letter text.
Calibre displays the fixed-format epub and the sitelen pona font properly on both Mac and Windows.
Apple Books displays the epub properly on the Mac.
I am now thinking that it may be time to completely rethink my epubs and implement them as reflowables with the pictures inline. This will require issuing new ISBNs for those ebooks that I have issued as fixed-pormat epubs,