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A document reference must include the identifier of the reference document (as specified in the referenceDocumentId attribute) to indicate which document is being referenced. If needed, the document reference may also include one or more "page references" (each specified in the pageRefs attribute) to indicate the relevant page or pages within the reference document. A document reference that does not include any page references is a reference areference to the document as a whole. In general, there are two types of document reference:
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Multiple page references may be created for a single document reference if more than one type of page reference is required (e.g., reference to both a set of individual page numbers and a range of page numbers), if more than one range of pages needs to be specified, or if the sponsor prefers to assign different labels for page references of the same type.