13. The non-transitory computer readable storage medium of claim 10 , wherein adding the mapping between an identified source document content item and a target document content item to the index stored by the electronic publishing platform comprises: identifying a location of the identified source document content item in the source document; identifying a location of the target document content item in the target document; and storing a mapping from the identified location of the source document content item to the identified location of the target document content item.
13. The non-transitory computer readable storage medium of claim 10 , wherein adding the mapping between an identified source document content item and a target document content item to the index stored by the electronic publishing platform comprises: identifying a location of the identified source document content item in the source document; identifying a location of the target document content item in the target document; and storing a mapping from the identified location of the source document content item to the identified location of the target document content item. 15. The non-transitory computer readable storage medium of claim 13 , wherein identifying the location of the identified source document content item and the location of the target document content item comprises: retrieving a document part identifier of the identified source document content item and a document part identifier of the target document content item, each document part identifier specifying the location of the corresponding content item.