Bug https://bugs.webkit.org/show_bug.cgi?id=229556 exposes the root plugin object for NSAccessibilityUIElementsForSearchPredicateParameterizedAttribute requests with SearchKey::AnyType. However, we should also support searching of elements inside the plugin tree. For example, if the underlying plugin is a PDF that has a control, and we receive a request with SearchKey::Control criteria, we should be able to return that PDF control.
To do this, we'll either need to perform the plugin tree traversal and matching ourselves, or ask the plugin to do it in some standard way, since the plugin could represent anything (i.e. not just PDFs).