Sorry I misinterpreted your issue. I tried to effect the outcome you want in various online regex test sites, and had mixed results with the uppercase function. I found that this pattern worked:
{(\w+)}
but whether \U\1 or any variation on that would produce a capitalized value from within the {}s was dependent on the on the site. Might as well post in the Bug Hunt forum in case there’s something that Keith can do about it.
Online sites I’ve tried (couldn’t find an online COCOA or SWIFT regex test site):
regexpal.com/
rubular.com/
regex101.com/r/tylTyS/1