This guidance section will cover the following roles, states, and properties:

• alert
• log
• marquee
• status
• timer
• aria-atomic
• aria-busy
• aria-live
• aria-relevant

It should also explain what kinds of updates the spec says should trigger a live region. @JAWS-test asked about the following list of possibilities and concerns in issue #1138.

• Insert into DOM
• Remove from DOM
• add role=alert to an existing node
• Change visibility (display:none, hidden, aria-hidden)
• Change the position (e.g.: left:100px)
• Change the color (e.g.: color:red)
• Change the size (e.g. width:100px)
• Change transparency (e.g. opacity:0;)

However, the output differs depending on whether these changes are made to the parent element, the element with role=alert, a direct child element, or a nested descendant element.
The output also varies depending on which Javascript method is used to insert element nodes into the DOM.

When working on this issue, there is some old content that may be useful in the file aria-practices-DeletedSectionsArchive.html.
The relevant section can be seen here:
https://rawgit.com/w3c/aria-practices/master/aria-practices-DeletedSectionsArchive.html#docmgt