 Unlike the other networks, which rigidly grant exclusivity within a market, some markets may contain multiple PBS stations; the network coordinates a "Program Differentiation Plan" that promotes variances in programming between the primary and secondary member stations.A single member may also operate a secondary schedule as a complement to their main schedule, either on a digital subchannel, or in rarer cases, a co-owned sister station (such as WGBH's WGBX).A more straightforward equivalent to a regional variation in North American broadcasting is a semi-satellite—a co-owned re-broadcaster of a television station that is used to extend its range into a different portion of a market (typically if the main signal is not strong enough to reach it), or a different one entirely, but has more variation in programming than a straight rebroadcaster.