{
  "id": "UBL-SR-52",
  "country": "EU",
  "syntax": "ubl",
  "group": "syntax",
  "severity": "fatal",
  "severity_note": "fatal, from the Flag column of the Peppol BIS Billing 3.0 UBL rules index retrieved 2026-10-18.",
  "spec": "Peppol BIS Billing 3.0, May 2026 release, EN 16931 model bound to UBL",
  "statement": "Document reference shall occur maximum once",
  "statement_lang": "en",
  "context": "cac:InvoiceLine | cac:CreditNoteLine",
  "test": "count(cac:DocumentReference) <= 1",
  "meaning": "The document reference shall occur at most once. The statement has no period and says shall. It is 43 characters. The flag is fatal. The context is an invoice line or a credit note line. The published test does not wrap the count in parentheses. It counts the document reference. The count comparison has a space before <= and a space after it.",
  "fix": "Send at most one document reference on a line.",
  "example_fail": "An invoice line has two document references.",
  "example_pass": "An invoice line has one document reference, or none.",
  "example_note": "Illustration of the condition in the official statement. Not an example published by the source.",
  "source_url": "https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/UBL-SR-52/",
  "source_retrieved": "2026-10-18",
  "last_verified": "2026-10-18"
}