any discussion of "what .epub supports" is dishonest dialog.

because the truth is that different .epub viewer-programs
"support" different subsets of the "official standard", and
thus the _reality_ of the format is that it's one huge mess,
a "standard" that's been embraced and extended to death,
whenever it wasn't locked-down with d.r.m. to begin with.

and that is exactly how the corporate publishers _want_ it.

because they're trying to stave off the revolution that will
short-circuit their cash-registers and ruin their business.

so what are they doing with .epub?  why, coming out with
_a_3.0_version_, of course, the better to boggle you with.
you think things were confusing and fragmented _before_?
well let's throw audio and video into the mix too, because
the last decade of the web _proved_ they cause infighting.
throw in some javascript, and html5, maybe flash as well,
in order to _ensure_ that e-books are a nasty experience.

it's no accident that amazon outpaced i.d.p.f. even while
using a format that was supposedly "inferior" to .epub...

but the end-run is inevitable, so all i.d.p.f. can do is stall it.

study the "history" all you want, most especially if you want
to distract people from _the_future_.  but if you want to go
_forward_, we need _a_clean_break_ from crap like .epub...

-bowerbird