# DT-CIUS-PT-121

Source: https://xmlvalid.com/rules/DT-CIUS-PT-121

> The BT-134 does not meet the defined format: YYYY-MM-DD.

- Level: error
- Rule sets: CIUS-PT rules (Portugal, UBL) 2.1.1
- Context: `//ubl:Invoice/cac:InvoiceLine/cac:InvoicePeriod/cbc:StartDate | //cn:CreditNote/cac:CreditNoteLine/cac:InvoicePeriod/cbc:StartDate`
- Test: `matches(.,'^((\d{4})-(\d{2})-(\d{2}))$')`

Validate a document against these rules: https://xmlvalid.com/validate