W3 Accessibility Guidelines Original

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; and
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.

W3 Accessibility Guidelines alt1

2.2 Pause, Stop, Hide

If web content moves, blinks, scrolls, or updates automatically, all of the following are true: (Level A)

Moving, blinking, scrolling: If moving, blinking or scrolling information starts automatically, lasts more than five seconds, or is presented at the same time as other content, there’s a way for the user to pause, stop, or hide the information – unless it’s an activity where the movement, blinking or scrolling is essential.
Auto-updating: If information updates automatically, starts automatically and is presented at the same time as other content, there is a way for the user to pause, stop, hide, or control the frequency of the update – unless it’s an activity where the auto-update is essential.

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

Note 2: Because content that fails this success criterion can interfere with a person’s ability to use anything else on the same webpage, all content must meet this success criterion, even content used to meet other success criteria. See Conformance Requirement 5: Non-Interference.

Note 3: Content that’s updated periodically by software or streamed to the user agent isn’t required to preserve or present information that’s generated or received when the content is paused. This may not be feasible, and could mislead users.

Note 4: An animation that happens only when users can’t interact with web content, such as to indicate progress during a preload, can be considered essential if the lack of movement could confuse users or cause them to think that content is frozen or broken.