Updated note to be normative

Author: vmpstr

css-contain-2/Overview.bs

@@ -1590,13 +1590,13 @@ the rendering state changes and the element either becomes or stops being
 
 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>
+Note that elements in ''content-visibility: auto'' subtrees remain semantically
+relevant even for elements that [=skip its contents=]. This means that it is
+inappropriate to use this signal to indefinitely skip DOM updates in the
+subtree that is skipped. Instead, it should be used to deprioritize updates,
+but ensure that the content remains semantically relevant and reasonably
+up-to-date. This is particularly important for assistive technologies which
+consume this content even when the ancestor is set to [=skip its contents=].
 
 Restrictions and Clarifications {#cv-notes}
 -------------------------------------------