SemanticsNode.root constructor

SemanticsNode.root({Key key, VoidCallback showOnScreen, SemanticsOwner owner })

Creates a semantic node to represent the root of the semantics tree.

The root node is assigned an identifier of zero.

Implementation 

SemanticsNode.root({
  this.key,
  VoidCallback showOnScreen,
  SemanticsOwner owner,
}) : id = 0,
     _showOnScreen = showOnScreen {
  attach(owner);
}