Aha!
https://www.mobileread.com/forums/sho...d.php?t=190723
oohhhhh.... KF8.
I think they've also done something with the way table cells now span better across pages rather than just cut off. I was using that for a kind of keep-together for image captions. Looks like I might be able to do it properly on the Kindle now!!
Also... and I need to check, I think that it might affect the media queries. I noticed that I couldn't modify a class when using amzn-mobi but that might just be me.
This is all very exciting!