import re

CAS_RX = re.compile(r"^\d{2,7}-\d{2}-\d$")
DTXSID_RX = re.compile(r"^DTXSID\d{7,}$")

def is_cas(s: str) -> bool:
    return bool(CAS_RX.match((s or "").strip()))

def normalize_cas(s: str) -> str:
    return (s or "").strip()

def is_dtxsid(s: str) -> bool:
    return bool(DTXSID_RX.match((s or "").strip()))