OP_LOOK_BEHIND   1527 regcomp.c            r = add_opcode(reg, OP_LOOK_BEHIND);
OP_LOOK_BEHIND   6237 regcomp.c        { OP_LOOK_BEHIND,          "look-behind",          ARG_SPECIAL },
OP_LOOK_BEHIND   6516 regcomp.c          case OP_LOOK_BEHIND:
OP_LOOK_BEHIND   3006 regexec.c          CASE(OP_LOOK_BEHIND)  MOP_IN(OP_LOOK_BEHIND);