bottom of the page the footnote appears on, trailing onto the next page if necessary without extending to the next paragraph until the page after the footnotes are done, and with the footnotes stored at the end of the book.

This is not me (per say), this is… I think you use KoReader? I do and I make my EPUBs with it in mind, and if I’m unsure I’ll test things on it. But it’s nothing more than the internal structure being tagged correctly for this to work in e.g. KoReader. Calibre will do a popup, and I mention that because these two are in my mind in one category of how readers deal with footnotes, the other category (at least that I know of) is that they… don’t, the user has to click the footnote (which is a link) and be taken to the footnote (and the somehow get back to the previous location). And I try to keep both in mind, and make something that will hopefully work for both of them. And then there is pandoc in the back of my mind, which understands footnotes (again when correctly tagged) but with at minimum the caveat that the footnote has to be internally in the same file (epubs are just ZIP files with primarily html files inside) and so should I keep the footnotes at the end of each chapter like I’ve done sometimes, but then in that mobileread thread someone was complaining “If there is anything I can’t stand, it is getting to the end of a chapter’s actual content and finding page after page of footnotes clogging it up before the next chapter” asdasjidbsoidjfhgasdoiufghasdoiufha<sdlfkhsidlofhjvasodufhiasdlifuh

And this is just footnotes, don’t get me started on other shit. Like, say you want to make a leader, you know, a thing that has existed for probably decades in print, support for some kind of it exists in CSS3, but KoReader does not support that IIRC. And that leads me to one of the problems, HTML/CSS engines because (for example) KoReader uses the CoolReader engine, which is a custom engine rather than like Chromium or Firefox or Safaris engines, which one the one hand is good, but leads to incomplete and differing completenes of implementation of HTML/CSS stuff. It’s like what I’ve heard the fucking 90s were all over again! And I have no idea what other weird HTML/CSS engines are out there in other readers, so who knows what I am doing that is actually not working on someones tablet.