Something I don't know about after all these years...

[MacMillan of Rathdown]

What is the Scottish tradition when someone marries into a family with a non-clan-affiliated surname? Are the children relegated to a tartan-less existence?

Basically it is up to the individual. Let's say Moira Campbell from Loch Fyne married Mr. John DeGrazzio and came to live in Burbank, California. Their children might have no interest in things Scottish, being happy to belong to the Sons of Italy, or the Native Sons of the Golden West. On the other hand, they might want to assert their Scottishness, in which case they could go the whole hog and take their Mother's maiden name, or they could simply honour the "quaint custom" of wearing their Mother's tartan.

I mean, surely there are modern born-and-raised Scottish Highlanders who carry names other than the traditional clan-affiliated names, but consider themselves Highlanders and wear an occasional kilt. Do they default to regional tartans?

When this happens (as it does all the time) their choices are pretty straight forward-- they can wear their Mother's tartan and, if asked, simply reply with something like, "My Mother's people are Campbells from around Loch Fyne." Or they can wear one of the "universal" tartans, or a district tartan, or whatever they want. Generally speaking, in Scotland, no one comes up to you and asks about your tartan-- it is assumed that you are wearing a tartan to which you have some attachment, and that's an end to it.

In Scotland people generally have about the same interest in someone's tartan as people in Texas have about someone's blue jeans. In other words, it no big deal what someone else is wearing.