code: public WriteConcern withW(final String w) {
          notNull("w", w);
          return new WriteConcern(w, wTimeoutMS, fsync, journal);
      }
docs: Constructs a new WriteConcern from the current one and the specified tag-set based value for w
  
  @param w tag set, or "majority", representing the servers to ensure write propagation to before acknowledgment.  Do not use string
  representation of integer values for w
  @return the new WriteConcern
  @see #withW(int)
  @mongodb.driver.manual tutorial/configure-replica-set-tag-sets/#replica-set-configuration-tag-sets Tag Sets