$ perl -Mre=debug -ce '/[a-z-[bc]]/'
Compiling REx "[a-z-[bc]]"
Final program:
   1: ANYOF[\-[a-z][] (12)
  12: EXACT <]> (14)
  14: END (0)
anchored "]" at 1 (checking anchored) stclass ANYOF[\-[a-z][] minlen 2
-e syntax OK
Freeing REx: "[a-z-[bc]]"