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                                                    382
           CHAPTER 4                                                                      Graphics



           manipulate the state of optional content groups based on external factors such as
           current system language settings or zoom level. Document authors can use usage
           application dictionaries to specify which entries in the usage dictionary should be
           consulted to automatically set the state of optional content groups based on such
           factors. Usage application dictionaries are listed in the AS entry in an optional
           content configuration dictionary (see Table 4.51). If no AS entry is present, states
           are not automatically adjusted based on usage information.

           A usage application dictionary specifies the rules for which usage entries should
           be used by viewer applications to automatically manipulate the state of optional
           content groups, which groups should be affected, and under which circumstanc-
           es. Table 4.53 shows the entries in a usage application dictionary.

           Note: Usage application dictionaries are only intended for use by interactive viewer
           applications, not for applications that use PDF as final form output (see “Determin-
           ing the State of Optional Content Groups” on page 385 for more information).

                           TABLE 4.53 Entries in a usage application dictionary
KEY             TYPE          VALUE

Event           name          (Required) A name defining the situation in which this usage application dictio-
                              nary should be used. May be View, Print, or Export.

OCGs            array         (Optional) An array listing the optional content groups that should have their
                              states automatically managed based on information in their usage dictionary
                              (see “Usage and Usage Application Dictionaries” on page 380). Default value: an
                              empty array, indicating that no groups are affected.

Category        array         (Required) An array of names, each of which corresponds to a usage dictionary
                              entry (see Table 4.52). When managing the states of the optional content groups
                              in the OCGs array, each of the corresponding categories in the group’s usage dic-
                              tionary should be considered.

           The Event entry specifies whether the usage settings should be applied during
           viewing, printing, or exporting the document. The OCGs entry specifies the set of
           optional content groups to which usage settings should be applied. For each of
           the groups in OCGs, the entries in its usage dictionary (see Table 4.52) specified
           by Category are examined to yield a recommended state for the group. If all the
           entries yield a recommended state of ON, the group’s state is set to ON; otherwise,
           its state is set to OFF.

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