An embodiment of a method includes receiving a selection of an original content item, deriving a supplemental content item from the original content item, designating a unique identifier to the supplemental content item, and inserting a reference including the unique identifier into the primary document. A system includes a candidate content item repository having one or more content items that can be included in a structured electronic document, a copy module configured to derive a base supplemental content item from a selected one of the candidate content items and further configured to designate a unique identifier for the base supplemental content item, and a document editor configured to receive the unique identifier and insert the unique identifier into a reference to the base supplemental content in the primary document.