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                                                   648
          CHAPTER 8                                                           Interactive Features




                          TABLE 8.43 Entries common to all action dictionaries
KEY        TYPE                    VALUE

Type       name                    (Optional) The type of PDF object that this dictionary describes; if
                                   present, must be Action for an action dictionary.

S          name                    (Required) The type of action that this dictionary describes; see Table 8.48
                                   on page 653 for specific values.

Next       dictionary or array     (Optional; PDF 1.2) The next action or sequence of actions to be per-
                                   formed after the action represented by this dictionary. The value is either
                                   a single action dictionary or an array of action dictionaries to be per-
                                   formed in order; see below for further discussion.

          The action dictionary’s Next entry (PDF 1.2) allows sequences of actions to be
          chained together. For example, the effect of clicking a link annotation with the
          mouse might be to play a sound, jump to a new page, and start up a movie. Note
          that the Next entry is not restricted to a single action but may contain an array of
          actions, each of which in turn may have a Next entry of its own. The actions may
          thus form a tree instead of a simple linked list. Actions within each Next array are
          executed in order, each followed in turn by any actions specified in its Next entry,
          and so on recursively. Viewer applications should attempt to provide reasonable
          behavior in anomalous situations. For example, self-referential actions should not
          be executed more than once, and actions that close the document or otherwise
          render the next action impossible should terminate the execution sequence.
          Applications should also provide some mechanism for the user to interrupt and
          manually terminate a sequence of actions.

          PDF 1.5 introduces transition actions, which allow the control of drawing during
          a sequence of actions; see “Transition Actions” on page 670.

          Note: No action should modify its own action dictionary or any other in the action
          tree in which it resides. The effect of such modification on subsequent execution of
          actions in the tree is undefined.


    8.5.2 Trigger Events

          An annotation, page object, or (beginning with PDF 1.3) interactive form field
          may include an entry named AA that specifies an additional-actions dictionary
          (PDF 1.2) that extends the set of events that can trigger the execution of an ac-

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