# Accessibility Regressions

Widgetbook Cloud compares the semantics tree of every scenario between the `base` and the `head` build and reports each difference as an **accessibility change**.
The semantics tree is what screen readers read, so a change to the tree is a change to how the app works for people relying on assistive technologies.

Changes reported:

- A `Semantics` label, hint, or tooltip that disappeared.
- A role that changed, for example from a button to plain text, or a heading that lost its level.
- Elements added to or removed from the tree.
- Elements that changed position among their siblings, which changes the reading order.

## Reading a Change

The **Accessibility Changes** section sits below the visual comparison on a scenario's diff.
It appears whenever the semantics tree differs, even when both screenshots are identical.

<Image src="/assets/cloud/accessibility/scenario-diff-accessibility.png" caption="Accessibility changes and violations on a scenario diff" zoom />

Each row is one element, showing its path in the tree, the type of change, and the properties that differ.
Hovering a row highlights the element's region on both screenshots.

| Type        | Meaning                                                                                      |
| ----------- | -------------------------------------------------------------------------------------------- |
| **Added**   | The element exists in the `head` build only.                                                  |
| **Removed** | The element exists in the `base` build only.                                                  |
| **Changed** | The element exists in both builds, but at least one property differs.                         |
| **Moved**   | The element's position among its siblings changed, which changes the assistive reading order. |

Expanding a changed element shows the affected properties side by side:

| Property | Previous     | Current      |
| -------- | ------------ | ------------ |
| label    | `Basket: 0$` | `Basket: 1$` |

Compared properties: `label`, `value`, `hint`, `tooltip`, `role`, `headingLevel`, `textDirection`, `validationResult`, `inputType`, `identifier`, `actions`, and `flagsCollection`, which carries the semantics flags such as `isButton`, `isHeader`, or `isSelected`.

Role is weighted when matching elements rather than required, so an element whose role changed is reported as a single **Changed** row with a `role` property.

Geometry is used to match elements between the two builds, but never reported as a change.
A component that only moved or resized produces no accessibility changes, which keeps layout shifts out of this section.

## Reviewing a Change

A scenario joins the pull request's change set when the screenshot changed **or** the semantics tree changed, so an accessibility change surfaces even when both screenshots are identical.

Accessibility changes are reviewed like any other change on a scenario.
See [Reviews](/cloud/reviews).

Rules that grade a single build instead of comparing two are covered on [Accessibility Violations](/cloud/accessibility/violations).