The alert role - ARIA Reference Guide

Composites
Represent containers for navigating interactive descendants.
Landmarks
Represent top-level sections of a page, relevant to a specific purpose, that a user may want to scan for quickly and could appear in a site map or table of contents.
Live Regions
Represent dynamic content or announcements, typically updated as a result of an external event when user focus may be elsewhere.
Structures
Represent non-interactive parts of a page that organize content into coherent units.
Widgets
Represent focusable, interactive elements.
Windows
Represent inner windows that are children of the main web document.

WAI-ARIA spec HTML-ARIA spec

Live Region(opens in new window)Flow Content(opens in new window)

Description

A type of live region with important, and usually time-sensitive, information. Alerts are used to convey messages that may be immediately important to users.

Allowed Content

Flow content but with no main element descendants.

HTML Elements with Implicit ARIA Role

(None)

Allowed HTML Elements

section
div, span, p, other elements that can receive any role