Split string by capital letter.

[wlwl2]

https://stackoverflow.com/questions/1097901/regular-expression-split-string-by-capital-letter-but-ignore-tla

((?<=[a-z])[A-Z]|[A-Z](?=[a-z]))

Unicode-aware:
((?<=\p{Ll})\p{Lu}|\p{Lu}(?=\p{Ll}))

handles:

TodayILiveInTheUSAWithSimon
USAToday
IAmSOOOBored

yielding:

Today I Live In The USA With Simon
USA Today
I Am SOOO Bored