IE8b1 — expressions support
So IE started filtering values in expressions since IE6, and now IE8b1 in both modes doesn't even allow you to use object property accessors (both dot and square brackets notations — see testcase). So in IE8b1 in expressions you can only use plain string values in your expressions (which is not handy at all) or call externally defined functions.
I can't help thinking of any other reason for disabling this except for protecting from potential XSS threat that I described in the previous post.
Also in IE8b1 expressions are not reevaluated on mouseover event (see testcase), but onscroll still fires
document.recalc (this again seems to be left intentionally in order to support all cludges that were invented to implement for example non-existent position: fixed CSS rule).
Bottom line, if you have expressions used in your CSS code, don't wait — separate all the stuff you do there to JS functions and just call these functions from your expressions.