Nice wrench you threw into that train of argument Diap - I was on a roll!!
Of course "content" is supported in epub's - otherwise all we would have is structure and styling!!
However the "content property" appears in the required subset properties list ePub 2.01
under "Generated Content, Automatic Numbering, and Lists".
Strangely it has a note after it:
 Must not be used within a style sheet whose @media value is other than aural.
That obviously doesn't make sense if you are not using an aural style sheet, so I'm not sure why it would be in the Generated Content section instead of the Aural Stylesheet section???
I do know that the content property is described as part of the :before and :after pseudo elements in both CSS2.0
(section 11.1) and CSS2.1 (section 12.1-12.2)
The 'content' property, in conjunction with these pseudo-elements, specifies what is inserted.
It is saying that the content property is inherent in the use of the :before and :after elements...you can't define them without the content property.
If you ask me, that would seem to imply that if the pseudo-elements MUST be supported, then the content property MUST be included...