The role description of this Node.
Noramlly, when a role is provided for a node, the screen reader speaks the role as well as the contents of the node. When this value is set, it is possbile to override the default. This is useful because the set of roles is predefined. For example, it is possible to set the role of a node to be a button, but have the role description be arbitrary text.
Node.
@defaultValue null
Diagram: Node