Wikipedia is an interesting source -- very helpful but often not very authoritative. According to an article stub on the Royal Stewart tartan, it says that the Royal Stewart is the personal tartan of Queen Elizabeth II. Further, it claims:

It is said to be appropriate for all subjects of Elizabeth to wear the Royal Stewart tartan[citation needed], much in the same way that clansmen may wear the tartan of their clan chief.
Is this true? What is the source of this idea? When wikipedia says "It is said" and there is no citation, it may as well be my favourite Japanese bartender who said it... Question is, is it true?

Next question. IF we were to assume the above to be true, could the same thing be said about variations on the Stewart tartan? I.e. would it be appropriate for all of Elizabeth's subjects to wear, say, a Black Stewart? Dress Stewart? Hunting Stewart? (I know that these are considered universal tartans so anyone can wear them regardless but I'm asking about appropriateness as a function of the claim in quoatations)...

Final question -- a little farther from the above. I've read numerous times in this forum that some people feel that it's appropriate to write a request to a clan chief before going ahead and wearing that clan's tartan. For those who feel this way, what would be the appropriate course of action in the case of an armigerous clan (a clan with no chief) such as the Stewart clan?

Thanks, guys. Apologies if any of this has been asked/answered before. I did use the search button.