documentation. For example, one repository may only commit to 
preserving the textual content of a document and not its exact appearance on a screen. 
Another may wish to preserve the exact appearance and layout of textual documents, while 
others may choose to keep the units of the measurement of data fields and to normalize the 
data during the ingest process. If unique identifiers are associated with digital objects before 
ingest, they may also be properties that need to be preserved. 
4.1.1.1 The repos