An unknown role is considered a bug, should never occur

third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp

 /*
 * Copyright (C) 2008 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 274 matching lines @@
 }
 
 AccessibilityRole AXLayoutObject::DetermineAccessibilityRole() {
   if (!layout_object_)
     return kUnknownRole;
 
   if ((aria_role_ = DetermineAriaRoleAttribute()) != kUnknownRole)
     return aria_role_;
 
   AccessibilityRole role = NativeAccessibilityRoleIgnoringAria();
-  if (role != kUnknownRole)
-    return role;
-
-  // These are layout containers added by blink
-  if (layout_object_->IsLayoutBlockFlow())
-    return kGenericContainerRole;
-
-  // If the element does not have role, but it has ARIA attributes or is an
-  // in-page link target, accessibility should fallback to exposing it as a
-  // generic container.
-  if (IsInPageLinkTarget() || SupportsARIAAttributes())
-    return kGenericContainerRole;
-
-  return kUnknownRole;
+  // Anything that needs to still be exposed but doesn't have a more specific
+  // role should be considered a generic container. Examples are
+  // layout blocks with no node, in-page link targets, and plain elements
+  // such as a <span> with ARIA markup.
+  return role == kUnknownRole ? kGenericContainerRole : role;
 }
 
 void AXLayoutObject::Init() {
   AXNodeObject::Init();
 }
 
 void AXLayoutObject::Detach() {
   AXNodeObject::Detach();
 
   DetachRemoteSVGRoot();
@@ skipping 2205 matching lines @@
 
 bool AXLayoutObject::ElementAttributeValue(
     const QualifiedName& attribute_name) const {
   if (!layout_object_)
     return false;
 
   return EqualIgnoringASCIICase(GetAttribute(attribute_name), "true");
 }
 
 }  // namespace blink