code: def letter_case_props(self, case, in_group, negate=False):
          
  
          # Use traditional ASCII upper/lower case unless:
          #    1. The strings fed in are not bytes
          #    2. And the the Unicode flag was used
          if not in_group:
              v = self.posix_props(("^" if negate else "") + ("upper" if case == _UPPER else "lower"), in_group=in_group)
              v[0] = "[%s]" % v[0]
          else:
              v = self.posix_props(("^" if negate else "") + ("upper" if case == _UPPER else "lower"), in_group=in_group)
          return v
docs: Insert letter (ASCII or Unicode) case properties.