Adds a defintion for essential text change

_rules/auto-update-text-efbfc7.md

@@ -3,7 +3,7 @@ id: efbfc7
 name: Text content that changes automatically can be paused, stopped or hidden
 rule_type: atomic
 description: |
-  This rule checks that for any text content that regularly changes automatically, there are instruments to pause, stop, or hide it or to control its changing frequency.
+  This rule checks that for any non-essential text content that regularly changes automatically, there are instruments to pause, stop, or hide it or to control its changing frequency.
 accessibility_requirements: # Remove whatever is not applicable
   wcag20:2.2.2: # Pause, Stop, Hide (A)
     forConformance: true
@@ -36,7 +36,7 @@ This rule applies to any [HTML element][] that has a [visible][] [text node][] a
 
 ## Expectation
 
-For each test target there is at least one set of [instruments][instrument], where each [instrument][] is in the same [web page][] as the test target or can be found in a [clearly labeled location][] from that [web page][], to achieve at least one of the following objectives:
+For each test target, the text change is not a[non essential text change][] or there is at least one set of [instruments][instrument], where each [instrument][] is in the same [web page][] as the test target or can be found in a [clearly labeled location][] from that [web page][], to achieve at least one of the following objectives:
 
 - pause and resume the change of the [visible text content][]; or
 - stop the change of the [visible text content][]; or
@@ -47,7 +47,6 @@ For each test target there is at least one set of [instruments][instrument], whe
 
 ## Assumptions
 
-- The auto-updating of the content is not [essential][], which is listed as valid exception to [Success Criterion 2.2.2: Pause, Stop, Hide][sc 2.2.2]. When the auto-updating of content is [essential][] this rule may produce incorrect results.
 - The content being changed automatically is information. If the automatically changing content is not information (for example, an ASCII rendered spinning icon that does not provide information on what time is left for a process to end or how much progress has been made) the rule might fail but the success criterion might still be satisfied.
 - Any [content][] changes are enabled by the content of the [HTML document][] the test target belongs to. Changes originating from any other sources (e.g. browser shortcuts, browser extensions, browser settings, user agents, external browser applications) are not considered.
 - All user actions are transmitted by the user agent to the [HTML document][]. If there are other event sources that result from a user action this rule might fail but the success criterion might still be satisfied.
@@ -310,7 +309,7 @@ This `span` element with text content that automatically changes multiple times
 [clearly labeled location]: #clearly-labeled-location 'Definition of clearly labeled location'
 [content]: https://www.w3.org/TR/WCAG21/#dfn-content
 [descendant]: https://dom.spec.whatwg.org/#concept-tree-descendant
-[essential]: https://www.w3.org/WAI/WCAG21/Understanding/pause-stop-hide.html#dfn-essential
+[non essential text change]: #non-essential-text-change 'Definition of non-essential text change'
 [flat tree]: https://drafts.csswg.org/css-scoping/#flat-tree 'Definition of flat tree'
 [f16]: https://www.w3.org/WAI/WCAG21/Techniques/failures/F16
 [g186]: https://www.w3.org/WAI/WCAG21/Techniques/general/G186

pages/glossary/non-essential-text-change.md

@@ -0,0 +1,22 @@
+---
+title: Non-Essential Text Change
+key: non-essential-text-change
+unambiguous: true
+objective: false
+input_aspects:
+  - Accessibility tree
+  - CSS styling
+  - DOM tree
+---
+
+A text change is considered non-essential if it occurs in any of the following scenarios:
+
+- **Carousels**: The text change is part of a fixed set of slides that is updated as part of a carousel; or
+- **Rolling Ads**: The text change occurs when an ad replaced with another ad on a timer; or
+- **Article feed**: The text change is part of a feed in which new articles are added as they become available such as news articles or posts on a social media site. This does not include chat feeds; or
+- **Live data**: The text change is an update of a live event or part of live information such as the scores of a sports match, an exchange rate, and weather measurements; or
+- **Countdown timer**: A timer that counts down to an event that occurs at a predetermined time.
+
+**Note**: Other scenarios in which a text change is not essential may exist, but are not covered by this definition. A text change is only "essential" when pausing, stopping or hiding it would fundamentally alter the meaning of information, or the functionality available on the page.
+
+**Note**: While pausing a live feed or live data does change the functionality, it is not a fundamental change. An equivalent alternative for live information would be information along with a particular date and time, to clearly distinguish it from live data. Similarly, a countdown timer is equivalent to providing the exact time at which the event occurs.