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Use case

Splitting off the discussion in flutter/engine#41681 into a standalone issue. That PR implements scopesRoute, namesRoute and label when all three are applied on the same node, in which case we use a combination of aria-label + role="dialog". However, scopesRoute and namesRoute do not have to be on the same node, which requires a different strategy.

Proposal

When scopesRoute and namesRoute are not on the same node, we look for the nearest scopesRoute ancestor of the namesRoute node and set aria-labelledby on the ancestor pointing down to the descendant.

Example:

Consider the following hypothetical structure of the Flutter semantics tree:

SemanticsObject(
  scopesRoute: true,
  children: [
    SemanticsObject(
      namesRoute: true,
      label: 'Dialog title',
    ),
  ]
)

This structure can be translated to ARIA tree as follows:

<flt-semantics id="flt-node-1" role="dialog" aria-labelled-by="flt-node-2">
  <flt-semantics id="flt-node-2" role="text" aria-label="Dialog title">
  </flt-semantics>
</flt-semantics>

See also:

• ARIA docs: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/dialog_role#labeling
• Android implementation: https://github.com/flutter/engine/blob/a0906bdfc845ee4321e624d24e07a579a7b66432/shell/platform/android/io/flutter/view/AccessibilityBridge.java#L1677