Originally Posted by pilotbob
So, isn't it possible two readers could render the same ePub file differently (a la HTML before there were specific standards)?
Since ePub is for reflowable content, it can clearly be rendered differently on different screen sizes. I always thought that stuff like CSS was optional, but apparently in ePub it is mandatory. In other words if you ignore the CSS (e.g. FBReader and to some extent ePub converted to MOBI) then it isn't ePub any more. In any case, there are two levels to the problem: a) can the format support the needed features and b) can the implementations on real devices support the needed features (either natively, or via conversion to, say, MOBI). It is a genuine advance that ePub, the format, can support many things that were not possible before. The jury is still out on whether ePub is "practical" on real devices smaller than a laptop/desktop. See Mobipocket announcements at IDPF conference
for screenshots of the (poor) state of the ePub rendering art today. By the way, the ePub from D. Appleton and Co. of Alice's Adventures in Wonderland
shows some of what ePub can do - see the text in the form of a mouse tail in the middle of Chapter 3 for example.
One way of looking at this is that the odds of going from PDF to a multi-device reflowable format are slim, but the odds of going from an ePub version (that displays very similarly to the PDF on a large screen) to smaller devices is much better - for one thing, it is already reflowable by design.