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          CHAPTER 10                                                          Document Interchange




                    TABLE 10.13 Additional dictionary entries for structure element access
KEY                 TYPE       VALUE

StructParent        integer    (Required for all objects that are structural content items; PDF 1.3) The integer
                               key of this object’s entry in the structural parent tree.

StructParents       integer    (Required for all content streams containing marked-content sequences that are
                               structural content items; PDF 1.3) The integer key of this object’s entry in the
                               structural parent tree.
                               Note: At most one of these two entries may be present in a given object. An object
                               can be either a content item in its entirety or a container for marked-content
                               sequences that are content items, but not both.

          For a content item identified by an object reference, the parent structure element
          can thus be found by using the value of the StructParent entry in the item’s object
          dictionary as a retrieval key in the structural parent tree (found in the ParentTree
          entry of the structure tree root). The corresponding value retrieved from the
          parent tree is a reference to the parent structure element (see Example 10.12).

          Example 10.12

                1 0 obj                             % Parent structure element
                   << /Type /StructElem
                      …
                      /K << /Type /OBJR             % Object reference
                            /Pg 2 0 R               % Page containing form XObject
                            /Obj 4 0 R              % Reference to form XObject
                         >>
                   >>
                endobj

                2 0 obj                           % Page object
                   << /Type /Page
                      /Resources << /XObject << /Fm4 4 0 R >>    % Resource dictionary
                                  >>                             % containing form XObject
                      /Contents 3 0 R             % Content stream
                      …
                   >>
                endobj

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