Music labels warn listeners of explicit lyrics.
Television tells viewers when shows contain sexual themes, violence or foul language.
Although past attempts at Net ratings have flopped, a coalition backed by Microsoft and AOL Time Warner is trying again. Its biggest challenge will be getting Web sites interested, because participation is voluntary. Although proponents consider rating systems more accurate than commercial filtering products, only a few hundred thousand Web sites currently carry ratings. Millions more do not. So for parents like Laurie Dodson who have configured their Web browsers to be guided by the ratings, the entire process backfires.