Originally Posted by DaleDe
It is very well defined what will happen and that is why the CSS standard says not to use it.
Not in 2.1 at least: "The page context has no notion of fonts, so 'em' and 'ex' units are not allowed. ". Since they are not alllowed it is unspecified what happens if they are used. It would be correct to turn off the reader when you see an em in a @page specification.