http://www.w3.org/TR/CSS21/generate.html#content Computed value: On elements, always computes to 'normal'. On :before and :after, if 'normal' is specified, computes to 'none'. Otherwise, for URI values, the absolute URI; for attr() values, the resulting string; for other keywords, as specified. But if you add some stylesheet like a {content: ""} p {content:none} This is applied to the elements, i.e. they are rendered empty (modulo some other bugs). Tested with Opera, Firefox, and Chromium: Opera has same behavior as KHTML, the other 2 follow the spec.
CSS3 says all fine: http://www.w3.org/TR/css3-content/#inserting3