The if statement in the dispatch implies we are in the idle state, so of course the active time will always be undefined. If this was cancelled via a call to cancel(), we can save the time at that point. Otherwise, just send 0.
CSSConditionRule.conditionText
CSSStyleSheet.addRule()
remove_rule()
CSSStyleSheet.replace()
CSSStyleSheet.replaceSync()
Element::directionality()
clip-rule