This flag indicates to the system that the accessibility service wants to access content of all interactive windows. An interactive window is a window that has input focus or can be touched by a sighted user when explore by touch is not enabled. If this flag is not set your service will not receive Android.Views.Accessibility.AccessibilityEvent.TYPE_WINDOWS_CHANGED events, calling AccessibilityServiceAccessibilityService.Windows will return an empty list, and Android.Views.Accessibility.AccessibilityNodeInfo.Window will return null.

Services that want to set this flag have to declare the capability to retrieve window content in their meta-data by setting the attribute NoType:android/R$attr;Href=../../../reference/android/R.attr.html#canRetrieveWindowContent to true, otherwise this flag will be ignored. For how to declare the meta-data of a service refer to AccessibilityService.ServiceMetaData.

[Android Documentation]