This reports whether this group's source filtering is operating in include mode, only listed source addresses are accepted, or exclude mode, all sources are accepted except those explicitly listed, the two source-filtering modes defined by IGMPv3/SSM. An admin implementing source-specific multicast for security or bandwidth reasons needs to confirm the group actually shows in(1) mode with the expected source list, since ex(2) mode would mean the device is accepting traffic from any source except a blocked list, a much more permissive and potentially less secure configuration. A value of ex(2) on a group intended to be tightly source-restricted would be a misconfiguration worth catching.