A Boolean value indicating whether VoiceOver should ignore the elements within views that are siblings of the receiver.
The default value for this property is NO. When the value of this property is YES, VoiceOver ignores the elements within the sibling views of the receiving view.
For example, in a window that contains sibling views A and B, setting accessibilityViewIsModal to YES on view B causes VoiceOver to ignore the elements in the view A. On the other hand, if view B contains a child view C and you set accessibilityViewIsModal to YES on view C, VoiceOver does not ignore the elements in view A.