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                                                    608
          CHAPTER 8                                                             Interactive Features



KEY            TYPE           VALUE

StructParent   integer        (Required if the annotation is a structural content item; PDF 1.3) The integer key
                              of the annotation’s entry in the structural parent tree (see “Finding Structure El-
                              ements from Content Items” on page 868).

OC             dictionary     (Optional; PDF 1.5) An optional content group or optional content member-
                              ship dictionary (see Section 4.10, “Optional Content”) specifying the optional
                              content properties for the annotation. Before the annotation is drawn, its visi-
                              bility is determined based on this entry as well as the annotation flags specified
                              in the F entry (see Section 8.4.2, “Annotation Flags”). If it is determined to be
                              invisible, the annotation is skipped, as if it were not in the document.


    8.4.2 Annotation Flags

          The value of the annotation dictionary’s F entry is an unsigned 32-bit integer con-
          taining flags specifying various characteristics of the annotation. Bit positions
          within the flag word are numbered from 1 (low-order) to 32 (high-order). Table
          8.16 shows the meanings of the flags; all undefined flag bits are reserved and must
          be set to 0.

                                      TABLE 8.16 Annotation flags
BIT POSITION   NAME            MEANING

1              Invisible       If set, do not display the annotation if it does not belong to one of the stan-
                               dard annotation types and no annotation handler is available. If clear, display
                               such an unknown annotation using an appearance stream specified by its ap-
                               pearance dictionary, if any (see Section 8.4.4, “Appearance Streams”).

2              Hidden          (PDF 1.2) If set, do not display or print the annotation or allow it to interact
                               with the user, regardless of its annotation type or whether an annotation
                               handler is available. In cases where screen space is limited, the ability to hide
                               and show annotations selectively can be used in combination with appearance
                               streams (see Section 8.4.4, “Appearance Streams”) to display auxiliary pop-up
                               information similar in function to online help systems. (See implementation
                               note 83 in Appendix H.)

3              Print           (PDF 1.2) If set, print the annotation when the page is printed. If clear, never
                               print the annotation, regardless of whether it is displayed on the screen. This
                               can be useful, for example, for annotations representing interactive pushbut-
                               tons, which would serve no meaningful purpose on the printed page. (See
                               implementation note 83 in Appendix H.)

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