Provides a secondary source that will be consumed if this stream completes without any elements passing by. As soon as the first element comes through this stream, the alternative will be cancelled. Note that this Flow will be materialized together with the SourceTOut, TMat and just kept from producing elements by asserting back-pressure until its time comes or it gets cancelled. On errors the stage is failed regardless of source of the error. '''Emits when''' element is available from first stream or first stream closed without emitting any elements and an element is available from the second stream '''Backpressures when''' downstream backpressures '''Completes when''' the primary stream completes after emitting at least one element, when the primary stream completes without emitting and the secondary stream already has completed or when the secondary stream completes '''Cancels when''' downstream cancels and additionally the alternative is cancelled as soon as an element passes by from this stream.

public static Source<T, TMat> OrElse<T, TMat>(
	this Source<T, TMat> flow,
	IGraph<SourceShape<T>, TMat> secondary
)

[<ExtensionAttribute>]
static member OrElse : 
        flow : Source<'T, 'TMat> * 
        secondary : IGraph<SourceShape<'T>, 'TMat> -> Source<'T, 'TMat>