use re 'debug';
my $braces = qr/(?<braces>\{ ([^\{\}] | (?&braces))*? \} )/x;

Compiling REx "(?<braces>\{ ([^\{\}] | (?&braces))*? \} )"
Final program:
   1: OPEN1 'braces' (3)
   3:   EXACT <{> (5)
   5:   MINMOD (6)
   6:   CURLYX[0] {0,32767} (29)
   8:     OPEN2 (10)
  10:       BRANCH (22)
  11:         ANYOF[\0-z|~-\377][{unicode_all}] (26)
  22:       BRANCH (FAIL)
  23:         GOSUB1[-22] (26)
  26:     CLOSE2 (28)
  28:   WHILEM[2/1] (0)
  29:   NOTHING (30)
  30:   EXACT <}> (32)
  32: CLOSE1 'braces' (34)
  34: END (0)
anchored "{" at 0 floating "}" at 1..2147483647 (checking floating) minlen 2 
Freeing REx: "(?<braces>\{ ([^\{\}] | (?&braces))*? \} )"