* cancellation of the operation so far. The only way to extract the value or exception from a step
 * is by declaring that step to be the last step of the pipeline. Nevertheless, we refer to the
 * "value" of a successful step or the "result" (value or exception) of any step.
 *
 * <ol>
 *   <li>A pipeline starts at its leaf step (or steps), which is created from either a callable

  private static String checkString(
      int length, int percent, String matchingChars, Random rand, boolean forceSlow, boolean web) {
    // Check whether we should ignore everything else and pull from the web.
    if (web) {
      StringBuilder builder = new StringBuilder(length);
      CharSamples sampler = new CharSamples(rand);
      for (int i = 0; i < length; i++) {