This class is a generic marker returned from a request into an executing flow
has completed processing, indicating a client response needs to be issued. An
instance of a ViewSelection subclass represents the selection of a concrete
response type. It is expected that callers introspect the returned view
selection instance to handle the response types they support.
View selections are returned as a result of entering a ViewState or
EndState , typically created by those states delegating to a
ViewSelector factory (a creational strategy). When a state of either
of those types is entered and returns, the caller into the web flow system is
handed a fully-configured ViewSelection instance and is
expected to present some form inteface to the client that allows for
interaction at that point within the flow.