Validate, normalize, parse, convert, generate, and classify securities identifiers. Auto-detect identifier type from any string. Calculate and restore check digits. Generate format-valid identifiers as test fixtures. Decode CFI codes to full ISO 10962:2021 classifications. Includes an opt-in ActiveModel/Rails validator that adds no runtime dependency. Supports ISIN, CUSIP, CEI, SEDOL, FIGI, LEI, IBAN, CIK, OCC, WKN, Valoren, CFI, FISN, BIC, and DTI.