Originally Posted by DaleDe
Personally I think a footnote should be done as <ref>This is a footnote</ref> and let the rendering program do it however it wishes. For example you might select the footnote and the program could pop up a window to display it in.
Actually that's exactly what the spec says, Reading Systems can choose how they will display footers and headers. It even mentions the possibility of popping these up separately.
The concept of having footnotes at the bottom of the page is an artifact of printed books. There's no reason why we can't have them as pop-ups. The content producer should be able to add an "display: oeb-page-foot" element describing the reference content above the first reference and have the Reading System take care of the details.
And all this is entirely supported by the spec:
Originally Posted by OPS Specification
Reading Systems, however, are free to present headers and footers either in special areas as usual for paper publications, or to make them available in another way. For example, a device with a small screen might instead pop them up on demand.
All I'm saying is that you could easily achieve "footnotes" with epub footers.