OP_KEEP          1504 regcomp.c        case ANCHOR_KEEP:           r = add_opcode(reg, OP_KEEP);           break;
OP_KEEP          6214 regcomp.c        { OP_KEEP,                "keep",                 ARG_NON },
OP_KEEP          2491 regexec.c          CASE(OP_KEEP)  MOP_IN(OP_KEEP);