[regex] case-splitting strings in unicode

[John Perks and Sarah Mount]

I have to split some identifiers that are casedLikeThis into their
component words. In this instance I can safely use [A-Z] to represent
uppercase, but what pattern should I use if I wanted it to work more
generally? I can envisage walking the string testing the
unicodedata.category of each char, but is there a regex'y way to denote
"uppercase"?

Thanks

John