A discussion in Surf’s Up, in the Navigating Web Pages lesson, covered a component of ARIA regions that makes it easier to navigate Web pages where they are used. Another use for ARIA is to announce text that changes on the screen for screen reader users. This is done with "live regions."
ARIA live regions are used on pages that update frequently, such as stock tickers and chat logs. If the ARIA property value is not set to "off," JAWS automatically detects when the content changes and speaks all content of the region, or only that which changed, depending on how the Web page was set up. This enables you to hear items that change on the page without you losing your place and without having to move there.
Live region property values can be set to be off, polite, or assertive. The majority of the time, Web page authors will use the polite value. This, of course, depends on the priority of what is happening in that spot on the screen. If the value is set to polite, your screen reader should not be interrupted. Instead, you will hear the changes at the next opportunity, such as when you have finished reading or when you have paused typing. If the value is set to assertive, that means the new information has a high priority, and your screen reader *should* notify you immediately.
The section below this paragraph contains some short text that changes every ten (10) seconds. You do not need to move to the area where the text is changing to read it. JAWS will read it for you once you have paused whatever you are doing.
The text just above this paragraph is the region that is set to change. In this example, all of the text on this part of the screen is replaced with new text each time, and all of the new text is spoken. However, some ARIA live regions may have text that stays the same as well as some text that does change. Do you want to hear all of the text in a region every time some of the text changes? Not always, but in some cases you do. Move on to the next page to get an idea of how this works.