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`AXPlatformNodeDelegate` provides a default implementation of `GetUniqueId()` which returns the same value (1) for all nodes. `AXPlatformNodeWin` relies on a unique ID being returned from this method in its `GetTargetFromChildID` method. In the world MSAA accessibility, each `HWND` may have a root `IAccessible` object associated with it. Events are fired by calling the `NotifyWinEvent` Win32 call and specifying: 1. The `HWND` (in our case, the one associated with our `WindowWin32`) 2. The target object (`OBJID_CLIENT` for the root `IAccessible` associated with that `HWND`) 3. A child identifier that uniquely identifies the target node in the tree This child identifier can be one of: * `CHILDID_SELF` for events targeting the root `IAccessible`. * A positive integer that specifies the index of a direct child of the root. * A negative integer which, when negated, specifies the unique ID of a child within the tree. On receipt of an accessibility event, `AXPlatformWin` (our `IAccessible` implementation) looks up the target `IAccessible` from the child ID specified on the event using its `GetTargetFromChildID` method and delegates the appropriate method call to that object. So, why is this implemented on our `AXPlatformNodeDelegate` subclass and not on `AXPlatformNodeWin` itself? Because the implementation of `AXPlatformNode::GetUniqueId()` delegates this lookup to the node delegate. As background, `AXUniqueId` automatically assigns itself a globally-unique value in its constructor; it tracks all used values in an internal static pool. Issue: https://github.com/flutter/flutter/issues/77838
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