driver-core/src/main/com/mongodb/WriteConcern.java
public WriteConcern withW(final String w) {
        notNull("w", w);
        return new WriteConcern(w, wTimeoutMS, fsync, journal);
    }
public WriteConcern withW(final String w) {
        notNull("w", w);
        return new WriteConcern(w, wTimeoutMS, fsync, journal);
    }
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