An alertdialog role is also used to alert the user with a message. Unlike alert role user can interact with the message. The initial focus goes to an element in the alert and user can navigate within the alert dialog box using keyboard and mouse. Developers should take care that the keyboard and mouse interactions are within the alert dialog when it is opened. Provide the alert message to the user with aria-describedby property to ensure that the message is conveyed to the screen reader user.
For an example when you delete a file or folder from the recycle bin in the windows operating system an alert is displayed asking the user “Are you sure You want to permanently delete this item? Providing the focus on “Yes” button. When you access the same dialog box using the JAWS or NVDA screen reader it will read the file name, file type etc but it will not read the message “Are you sure you want to permanently delete this item?”. Using ARIA-describedby property will help in overcoming such problems.