Parent documents are either the parent email to an email attachment or the parent document of an embedded document (e.g., an Excel spreadsheet embedded in a PowerPoint presentation).
Click the Parents button to list all parent documents of the current document. In this example, the current document has three parent emails--likely because the attachment was duplicated in three different emails. The following information is displayed for each: DISCO ID, filename, and an excerpt of first few words of the parent document.
Family navigation is only available for databases with this feature in crawl. With family navigation, you can navigate parent and child relationships without losing your place. In the Related documents section, hover over the documents in the Family section to see details about that document. Click the document to navigate to it.
By default, when you tag a parent document, all of the parent's children (e.g. attachments) are tagged.