f:DocumentReference date: minimum cardinality of 'date' is 1 content: maximum cardinality of 'content' is 1 f:DocumentReference/f:meta id: maximum cardinality of 'id' is 1 versionId: maximum cardinality of 'versionId' is 1 lastUpdated: maximum cardinality of 'lastUpdated' is 1 source: maximum cardinality of 'source' is 1 f:DocumentReference/f:content/f:attachment contentType: minimum cardinality of 'contentType' is 1 data: minimum cardinality of 'data' is 1