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                                                       849
           SECTION 10.4                                                       Page-Piece Dictionaries




                                  TABLE 10.5 Entries in a page-piece dictionary
KEY                       TYPE              VALUE

any application name      dictionary        An application data dictionary (see Table 10.6).
or well-known data type


                            TABLE 10.6 Entries in an application data dictionary
KEY                       TYPE              VALUE

LastModified              date              (Required) The date and time when the contents of the document,
                                            page, or form were most recently modified by this application.

Private                   (any)             (Optional) Any private data appropriate to the application, typically
                                            in the form of a dictionary.

           The LastModified entry indicates when this application last altered the content of
           the page or form. If the page-piece dictionary contains several application data
           dictionaries, their modification dates can be compared with those in the corre-
           sponding entry of the page object or form dictionary (see Table 3.27 on page 145
           and Table 4.45 on page 358), or the ModDate entry of the document information
           dictionary (see Table 10.2), to ascertain which application data dictionary corre-
           sponds to the current content of the page or form. Because some platforms may
           use only an approximate value for the date and time or may not deal correctly
           with differing time zones, modification dates are compared only for equality and
           not for sequential ordering.

           Note: It is possible for two or more application data dictionaries to have the same
           modification date. Applications can use this capability to define multiple or extend-
           ed versions of the same data format. For example, suppose that earlier versions of an
           application use an application data dictionary named PictureEdit, and later ver-
           sions of the same application extend the data to include additional items not previ-
           ously used. The original data could continue to be kept in the PictureEdit dictionary
           and the additional items placed in a new dictionary named PictureEditExtended.
           This allows the earlier versions of the application to continue to work as before, and
           later versions are able to locate and use the extended data items.

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