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A reference to a prior metadata version. This version must be present earlier in the same ODM file or in a previous file in the series. See the PriorFileOID attribute of the ODM element(Section 3.2, ODM).
When a metadata element such as an ItemDef is re-defined in a MetaDataVersion that includes a previous MetaDataVersion, any metadata element of the same type and with the same OID in a preceding MetaDataVersion is completely replaced. This includes all attributes and child elements. It also means that all attributes and child elements not present in the new definition are effectively deleted from the previous version.
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