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Definition of blinking

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In our WCAG2ICT discussions this week, as we looked at the glossary term blinking, we explored a UI convention that pops up more in desktop UIs than in the web: that of "throbbing". In some desktop UIs (I vaguely recall seeing this on a Macintosh with a particular default/OK button becoming available after a process finished), you can have an element that is "throbbing" through a range of colors, not simply blinking on/off. And while I've only seen this where there were two clear end states of the "throb" (e.g. slowly animating the background color of a button from light blue to dark blue through perhaps 20 or more steps), it isn't hard to imagine something that rotates through the color wheel such that there isn't a pair of clearly defined end "states" it is "throbbing" between.

There was disagreement within the TF as to whether (and which types of) "throbbing" was or was not an instance of "blinking". There was also separate discussion as to whether (and which types of) "throbbing" should be covered by SC 2.2.2.

I think that this should be clarified in Understanding WCAG.


2.2.2 READS:


2.2.2 Pause, Stop, Hide: For moving, blinking, scrolling, or auto-updating information, all of the following are true: (Level A)

  • Moving, blinking, scrolling: For any moving, blinking or scrolling information that (1) starts automatically, (2) lasts more than five seconds, and (3) is presented in parallel with other content, there is a mechanism for the user to pause, stop, or hide it unless the movement, blinking, or scrolling is part of an activity where it is essential; and0
  • Auto-updating: For any auto-updating information that (1) starts automatically and (2) is presented in parallel with other content, there is a mechanism for the user to pause, stop, or hide it or to control the frequency of the update unless the auto-updating is part of an activity where it is essential.

Note 1: For requirements related to flickering or flashing content, refer to Guideline 2.3.

Note 2: Since any content that does not meet this success criterion can interfere with a user's ability to use the whole page, all content on the Web page (whether it is used to meet other success criteria or not) must meet this success criterion. See Conformance Requirement 5: Non-Interference.

Note 3: Content that is updated periodically by software or that is streamed to the user agent is not required to preserve or present information that is generated or received between the initiation of the pause and resuming presentation, as this may not be technically possible, and in many situations could be misleading to do so.

Note 4: An animation that occurs as part of a preload phase or similar situation can be considered essential if interaction cannot occur during that phase for all users and if not indicating progress could confuse users or cause them to think that content was frozen or broken.


The purpose of this is to address two problems. One is an old problem that some screen readers no longer have with regard to text which is continually updated and jamming screen readers. The other is content which is visually active and distracting to users. Content that moves and continues to move over time or to in some other way attract attention without stopping can prevent some people from being able to use the page. Note that this provision only comes into effect when the animated information or item is in parallel with other content.

The intent is to stop the attention getting activity if it persists longer than five seconds (and is in parallel with other content). The terms "moving, blinking, scrolling, or auto-updating" were used to provide concrete terms describe this. You'll also note that the word animation is in one of the notes. The intent of this item was to choose a series of words that would together cover the wide range of animations or other visually attention grabbing dynamic behavior.

With regard to your question, and since this is the only place in WCAG 2.0 that the word blink is used, it would seem clear that the kind of behavior you referring to would be covered by the intention of the word blink. Anything that is moving from one state to another through any intermediate path would distracting and would fall under the intent.

With regard to your request to add something to our intent to make clear, we propose the following:

In Understanding SC 2.2.2 (Pause, Stop, Hide), add the following immediately before the sentence that begins "Content that is paused…":

"A button that slowly moves between different color states in a fashion that causes it to eventually cycle would qualify as blinking unless it did this so slowly that it was not immediately perceivable or distracting. In fact, the intent of this success criterion would be to require that the user be able to stop or pause any content that was visually distracting and that persisted for more than five seconds. Something that is changing in order to attract attention clearly would be included in the intent of this success criterion."