alt131 - 4:01 pm on Jul 6, 2011 (gmt 0)
Other user agents read and try to process the rule. It is not valid so triggers error handling. That may not cause a noticeable problem, but the issue is completely avoided by using a conditional comment.
It doesn't interfere with Firefox or Chrome which use the attribute selector just fine, so no need for conditional comments
... nor sending styles from a div in the body. ;)
don't make a habit of recommending IE expressions