<p>A Document Repository Actor initiates the Register Document Set transaction. This transaction allows a Document Repository Actor to register one or more documents with a Document Registry, by supplying metadata about each document to be registered. This document metadata will be used to create an XDS Document Entry in the registry. The Document Registry Actor ensures that document metadata is valid before allowing documents to be registered. If one or more documents fail the metadata validation, the Register Document Set transaction fails as a whole.</p><p> To support composite documents, an XDS Document may be a multipart document. The Document Repository must handle multi-part data sets as an  opaque entity . The Document Repository does not need to analyze or process its multi-part structure nor the content of any parts in the context of the XDS Integration Profile. </p>