What happens when a “browser event” occurs? The quick answer

Published: 5 December 2025

Have you ever wondered how browsers turn user interactions into a screen reader announcement?

Here’s a simple model that shows the key steps. This covers: an event firing, DOM updates, changes in the accessibility tree, and finally the AXEvent that reaches assistive technologies.

Steps that occur inside the browser

1. A user event occurs
   Click, key press, pointer movement, etc.

2. The browser processes the event
   It determines what was interacted with (hit-testing), applies default element behaviour, and updates internal state.

3. The browser updates layout or repainting if needed
   Only when something visual has changed — text, position, open/closed state, etc.

4. The browser updates the accessibility tree
   It synchronises accessibility information with DOM and layout changes, computing names, roles, states, relationships, and values.

5. The browser generates AXEvents
   Examples: value changed, state changed, focus changed, live region updated.

6. The browser sends AXEvents to the OS accessibility API
   Using the appropriate platform API:

   • AX API — macOS, iOS
   • UIA — Windows
   • ATK / AT-SPI — Linux

Steps that occur outside the browser

7. The OS accessibility API notifies assistive technology
   Screen readers subscribe to these OS-level notifications and receive them as events.

8. The assistive technology decides what to do
   Announce, queue, merge, interrupt, delay, or ignore the event based on its logic and user settings.