Multicasts the source sequence notifications through an instantiated subject into all uses of the sequence within a selector function. Each
subscription to the resulting sequence causes a separate multicast invocation, exposing the sequence resulting from the selector function's
invocation. For specializations with fixed subject types, see
Function): Factory function to create an intermediate subject through which the source sequence's elements will be multicast to the selector function.
subject(Subject): Subject to push source elements into.
Function): Optional selector function which can use the multicasted source sequence subject to the policies enforced by the created subject. Specified only if
Observable): An observable sequence that contains the elements of a sequence produced by multicasting the source sequence within a selector function.