anchor.diff:  
     /// Returns a stream of pairs of elements from the given pair of streams.  No
     /// elements from either stream are skipped and each element is used only
  -  /// once.  See also: `combineLatest`.
  +  /// once.  In `zip xs ys`, the `xs` stream is examined first.  See also:
  +  /// `pullOn`, `combineLatest`.
   #if DOC
     ///
     /// For example,
  
positive.code: 
    /// Returns a stream that runs the given job each time a value is requested
    /// before requesting the next value from the given stream.  If the given job
    /// fails, the returned stream also fails.
  #if DOC
    ///
    /// Reference implementation:
    ///
    ///> let rec beforeEach yJ xs =
    ///>   yJ >>. xs >>=* function Nil -> nil
    ///>                         | Cons (x, xs) -> cons x (beforeEach yJ xs)
  #endif
    val beforeEach: timeout: Job<_> -> Stream<'x> -> Stream<'x>
  
    /// Given a stream of dates, returns a stream that produces the dates after
  
negative.code: 
    /// Returns a stream that produces the same elements as the given stream, but
    /// delays each pulled element using the given job.  If the given job fails,
    /// the returned stream also fails.  `delayEach yJ xs` is equivalent to
    /// `zipWithFun (fun x _ -> x) xs (indefinitely yJ)`.  See also: `shift`.
  #if DOC
    ///
    ///>   input: 1        2 3   4        5
  