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       CHAPTER 10                                                          Document Interchange



                EMC                              % End of marked-content sequence
             …
          endstream
          endobj


       PDF Objects as Content Items

       When a structure element’s content includes an entire PDF object, such as an
       XObject or an annotation, that is associated with a page but not directly included
       in the page’s content stream, the object is identified in the structure element’s K
       entry by an object reference dictionary (see Table 10.12). Note that this form of
       reference is used only for entire objects. If the referenced content forms only part
       of the object’s content stream, it is instead handled as a marked-content sequence,
       as described in the preceding section.

                         TABLE 10.12 Entries in an object reference dictionary
KEY    TYPE           VALUE

Type   name           (Required) The type of PDF object that this dictionary describes; must be OBJR for an
                      object reference.

Pg     dictionary     (Optional; must be an indirect reference) The page object representing the page on
                      which the object is rendered. This entry overrides any Pg entry in the structure ele-
                      ment containing the object reference; it is required if the structure element has no such
                      entry.

Obj    (any)          (Required; must be an indirect reference) The referenced object.

       Note: If the referenced object is rendered on multiple pages, each rendering requires
       a separate object reference. However, if it is rendered multiple times on the same
       page, just a single object reference suffices to identify all of them. (If it is important
       to distinguish between multiple renditions of the same XObject on the same page,
       they should be accessed by means of marked-content sequences enclosing particular
       invocations of the Do operator rather than through object references.)


       Finding Structure Elements from Content Items

       Because a stream cannot contain object references, there is no way for content
       items that are marked-content sequences to refer directly back to their parent
       structure elements (the ones to which they belong as content items). Instead, a

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