Update November 5th 2008: this bug report is INVALID. For more info, consult the www-style email list discussion on [CSS2.1] Clarification on section 4.1.3 and the application of escaped newlines to identifiers

This line should be green.

Reference: (...) inside a string, a backslash followed by a newline is ignored (i.e., the string is deemed not to contain either the backslash or the newline).
coming from CSS 2.1, section 4.1.3 Characters and case

Firefox 3.0.3, NS 7.2, Seamonkey 1.x, Seamonkey 2.x, K-meleon 1.x, Galeon 2.0.7, Epiphany 2.22.3 all pass this test.

The W3C CSS validator will report a lexical error and an ensuing parsing error and that seems to be a bug with the W3C CSS validator. This issue has been reported accordingly as bug 6203 at W3C Bug / Issue Tracking Service.

HTML 4.01 Strict compliant Valid CSS!