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                                                  602
        CHAPTER 8                                                            Interactive Features



        Note: Viewer applications should save the state of optional content groups when a
        user enters presentation mode and restore it when presentation mode ends. This en-
        sures, for example, that transient changes to bullets do not affect the printing of the
        document.

        A navigation node dictionary (see Table 8.14) specifies actions to execute when
        the user makes a navigation request; for example, by pressing an arrow key. The
        navigation nodes on a page form a doubly linked list by means of their Next and
        Prev entries. The primary node on a page is determined by the optional PresSteps
        entry in a page dictionary (see Table 3.27).

        Note: It is recommended that a viewer application respect navigation nodes only
        when in presentation mode (see Section 8.3.3, “Presentations”).

                         TABLE 8.14 Entries in a navigation node dictionary
KEY    TYPE             VALUE

Type   name             (Optional) The type of PDF object that this dictionary describes; must be NavNode
                        for a navigation node dictionary.

NA     dictionary       (Optional) The sequence of actions to execute when a user navigates forward.

PA     dictionary       (Optional) The sequence of actions to execute when a user navigates backward.

Next   dictionary       (Optional) The next navigation node, if any.

Prev   dictionary       (Optional) The previous navigation node, if any.

Dur    number           (Optional) The maximum number of seconds before the viewer application should
                        automatically advance forward to the next navigation node. If this entry is not spec-
                        ified, no automatic advance should occur.

        A viewer application should support the notion of a current navigation node.
        When a user navigates to a page, if the page dictionary has a PresSteps entry, the
        node specified by that entry becomes the current node. (Otherwise, there is no
        current node.) If there is a request to navigate forward (such as an arrow key
        press) and there is a current navigation node, the following occurs:

        1. The sequence of actions specified by NA (if present) is executed.
          Note: If NA specifies an action that navigates to another page, the actions de-
          scribed below for navigating to another page take place, and Next should not be
          present.

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