Whether the semantics node is a live region.
A live region indicates that updates to semantics node are important. Platforms may use this information to make polite announcements to the user to inform them of updates to this node.
An example of a live region is a SnackBar widget. On Android, A live region causes a polite announcement to be generated automatically, even if the user does not have focus of the widget.
static const SemanticsFlag isLiveRegion = SemanticsFlag._(_kIsLiveRegionIndex)