as posted by macneighill
2. A clique; a sect, society, or body of persons; esp., a body of persons united by some common interest or pursuit; -- sometimes used contemptuously.
According to Webster's, Xmarks is a clan then! We are a body of persons united by a common interest or pursuit, and perhaps the some of the outside world, our ideas are held in a little contempt.

As well, what about a person that is a MacDonald because their ancestor was a random son of a man named Donald and bears no familial relation to anyone from the Isle of Skye or surrounding areas? I have no doubt that any of the Clan Societies that are related to the name MacDonald, even the ones that follow the "law" to a "T", would have a problem letting this brother into their midst, since his name was MacDonald. Any thoughts!