XAdES adds a QualifyingProperties element referenced by the XML signature: SignedProperties (signing time, signing certificate digest, signature policy, commitment type) and unsigned properties for timestamps and validation data. Levels mirror PAdES: B-B, B-T, B-LT, B-LTA. It is used for e-invoicing, public-sector filings and EU trusted lists themselves, which are XAdES-signed XML.
All XML-DSig pitfalls apply — canonicalization, reference resolution and signature wrapping — so validation should use mature libraries such as the EU DSS framework. The XAdES inspector shows signed properties and references.