According to the
official specs, the new
Kindle Paperwhite will support in-line popup footnotes. However, since the Kindle Publishing Guidelines haven't been updated yet, I'm wondering how they're supposed to be encoded.
Since Amazon has partial support for some HTML5/CSS3 and epub3 features, I did a test with the basic
Moby Dick epub 3 sample (the
footnote code is in preface_001.xhtml), but KindleGen reported lots of issues, which were most likely caused by other unsupported epub3 features.
I then extracted just the relevant page and created an epub2 test file that I compiled without problems with KindleGen, but in Kindle Previewer the popup footnote feature didn't work in Paperwhite mode, which didn't really surprise me.
Since Amazon has most likely added support for this feature in the recent 5.3.8 Paperwhite firmware update, I'd appreciate it if someone who has a Paperwhite with the 5.3.8 firmware could open my test file with it to find out if the footnote pops up, if you tap the 1.