anchor.diff:     * Combines a sequence of values by repeatedly applying [combine].
      *
      * Similar to [Iterable.reduce], this function maintains a value,
  -   * starting with the first element of the stream
  +   * starting with the first element of this stream
      * and updated for each further element of this stream.
      * For each element after the first,
      * the value is updated to the result of calling [combine]
  
positive.code:    * mapped to a new event.
     *
     * This acts like [map], except that [convert] may return a [Future],
     * and in that case, the stream waits for that future to complete before
     * continuing with its result.
     *
     * The returned stream is a broadcast stream if this stream is.
  
negative.code:   /**
     * The number of elements in this stream.
     *
     * Waits for all elements of this stream. When this stream ends,
     * the returned future is completed with the number of elements.
     *
     * If this stream emits an error,
     * the returned future is completed with that error,
     * and processing stops.
     *
     * This operation listens to this stream, and a non-broadcast stream cannot
     * be reused after finding its length.
     */
    Future<int> get length {
  