Add ContentVisibilityAutoStateChanged event

Author: vmpstr

css-contain-2/Overview.bs

@@ -1552,6 +1552,52 @@ Using ''content-visibility: auto''</h3>
 		will be forced to rely on the ''200px'' height estimate.
 	</div>
 
+Detecting ''content-visibility: auto'' state changes: the 'ContentVisibilityAutoStateChanged' event {#content-visibility-auto-state-changed}
+--------------------------------------------------------------------------------------------------------------------------------------------
+
+<pre class='idl'>
+[Exposed=Window]
+interface ContentVisibilityAutoStateChangedEvent : Event {
+  constructor(DOMString type, optional ContentVisibilityAutoStateChangedEventInit eventInitDict = {});
+  readonly attribute boolean skipped;
+};
+dictionary ContentVisibilityAutoStateChangedEventInit : EventInit {
+  boolean skipped = false;
+};
+</pre>
+
+<div class="attributes">
+
+Description of ContentVisibilityAutoStateChangedEvent attributes:
+
+: <dfn attribute for=ContentVisibilityAutoStateChangedEvent>skipped</dfn>
+:: Set to true if target changed state to [=skip its contents=], and false otherwise.
+
+</div>
+
+<div class="members">
+
+Description of ContentVisibilityAutoStateChangedEventInit members:
+
+: <dfn dict-member for=ContentVisibilityAutoStateChangedEventInit>skipped</dfn>
+:: See the description of the {{ContentVisibilityAutoStateChangedEvent/skipped}} attribute.
+
+</div>
+
+This event is fired on an element with ''content-visibility: auto'' style when
+the rendering state changes and the element either becomes or stops being
+[=relevant to the user=].
+
+This event is dispatched by posting a task at the time when the state change occurs.
+
+<p class=note>This event is a convenient way to track the state of
+''content-visibility: auto'' elements. By observing the event, the developer
+can to stop or start additional work within the affected subtree, such as DOM
+updates or canvas redraws. It is important to remember that
+''content-visibility: auto'' subtree elements are exposed to accessibility
+tooling. One must take care to ensure that the content remains sufficiently
+updated for assistive technology consumption.</p>
+
 Restrictions and Clarifications {#cv-notes}
 -------------------------------------------