Message

DocumentHash MUST resemble a SHA-256 hash value (32 byte HexString)

Context
ubl:Tender/cac:DocumentReference/cac:Attachment/cac:ExternalReference/cbc:DocumentHash
Test
matches(normalize-space(.),'^[a-fA-F0-9]{64}$')
Usage
/ t005:Tender / cac:DocumentReference / cac:Attachment / cac:ExternalReference / cbc:DocumentHash