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                                               798
      CHAPTER 9                                                         Multimedia Features



KEY          TYPE           VALUE

AN           dictionary     (Optional; PDF 1.7) An animation style dictionary indicating the preferred
                            method that viewer applications should use to drive keyframe animations
                            present in this artwork (see “3D Animation Style Dictionaries” on page 799).
                            Default value: an animation style dictionary whose Subtype entry has a value
                            of None.

      The Subtype entry specifies the format of the 3D stream data. The only valid val-
      ue is U3D, which indicates that the stream data conforms to the Universal 3D File
      Format specification (see Bibliography). PDF consumer applications must be pre-
      pared to encounter unknown values for Subtype and recover appropriately,
      which usually means leaving the annotation in its inactive state, displaying its
      normal appearance.

      Note: Applications are encouraged to follow the approach of falling back to the nor-
      mal appearance with regard to entries in other dictionaries that may take different
      types or values in future PDF versions than the ones specified here.

      The VA entry is an array containing a list of named present views of the 3D art-
      work. Each entry in the array is a 3D view dictionary (see Section 9.5.3, “3D
      Views”) that contains the name of the view and the information needed to display
      the view. The order of array elements is the order in which the views are present-
      ed in a user interface. The DV entry specifies the view to use as the initial view of
      the 3D artwork.

      Note: Default views can be specified in the following order of precedence: in the an-
      notation dictionary, in the 3D stream dictionary, or in the 3D artwork contained in
      the 3D stream.

      3D streams contain information that can be used by applications and scripts to
      perform animations and other programmatically-defined behaviors, from chang-
      ing the viewing orientation to moving individual components of the artwork. The
      OnInstantiate entry specifies a JavaScript script that is executed by applications
      that support JavaScript whenever a 3D stream is read to create an instance of the
      3D artwork. The Resources entry is a name tree that contains objects that can be
      used to modify the initial appearance of the 3D artwork. The 3D JavaScript inter-
      face for Acrobat is described in JavaScript for Acrobat API Reference (see the Bib-
      liography).

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