Compiling REx "%n    (?{%n         say %"before:\n\@- = (@-)\t\t %".scalar("...
synthetic stclass "ANYOF[\0-\11\13-\377][{unicode_all}]".
Final program:
   1: EVAL (3)
   3: BOL (4)
   4: OPEN1 (6)
   6:   GOSUB3[+19] (9)
   9: CLOSE1 (11)
  11: OPEN2 (13)
  13:   GOSUB3[+12] (16)
  16: CLOSE2 (18)
  18: EOS (19)
  19: EVAL (21)
  21: DEFINEP (23)
  23: IFTHEN (44)
  25:   OPEN3 'expr' (27)
  27:     OPEN4 (29)
  29:       REG_ANY (30)
  30:     CLOSE4 (32)
  32:     OPEN5 (34)
  34:       REG_ANY (35)
  35:     CLOSE5 (37)
  37:     EVAL (39)
  39:   CLOSE3 'expr' (44)
  41:   LONGJMP (43)
  43:   TAIL (44)
  44: END (0)
floating ""$ at 2..2147483647 (checking floating) stclass ANYOF[\0-\11\13-\377][{unicode_all}] minlen 2 with eval