CSSRule - Web APIs
csscounterstylerule cssrule.supports_rule 12 csssupportsrule cssrule.document_rule 13 cssdocumentrule cssrule.font_feature_values_rule 14 cssfontfeaturevaluesrule cssrule.viewport_rule 15 cssviewportrule cssrule.region_style_rule 16 cssregionstylerule cssrule.unknown_rule 0 cssunknownrule cssrule.charset_rule 2 csscharsetrule (removed in most browsers.) an up-to-date informal list of constants can be found on the csswg wiki.