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                                                   365
         SECTION 4.10                                                           Optional Content



KEY          TYPE            VALUE

Intent       name or array   (Optional) A single intent name or an array containing any combination of
                             names. PDF 1.5 defines two names, View and Design, that indicate the intended
                             use of the graphics in the group. Future versions may define others. A process-
                             ing application can choose to use only groups that have a specific intent and ig-
                             nore others.
                             Default value: View. See “Intent” on page 368 for more information.

Usage        dictionary      (Optional) A usage dictionary describing the nature of the content controlled by
                             the group. It may be used by features that automatically control the state of the
                             group based on outside factors. See “Usage and Usage Application Dictionaries”
                             on page 380 for more information.

         In its simplest form, each dictionary contains a Type entry and a Name for pre-
         sentation in a user interface. It may also have an Intent entry that describes its in-
         tended use (see “Intent” on page 368) and a Usage entry that describes the nature
         of its content (see “Usage and Usage Application Dictionaries” on page 380).

         Individual content elements in a document specify the optional content group or
         groups that affect their visibility (see Section 4.10.2, “Making Graphical Content
         Optional”). Any content whose visibility can be affected by a given optional con-
         tent group is said to belong to that group.

         A group is assigned a state, which is either ON or OFF. States are not themselves
         part of the PDF document but can be set programmatically or through the viewer
         user interface to change the visibility of content. When a document is first
         opened, the groups’ states are initialized based on the document’s default config-
         uration dictionary (see “Optional Content Configuration Dictionaries” on page
         375).

         In the typical case, content belonging to a group is visible when the group is ON
         and invisible when it is OFF. In more complex cases, content can belong to multi-
         ple groups, which may have conflicting states. These cases are described by the
         use of optional content membership dictionaries, described in the next section.


         Optional Content Membership Dictionaries

         As mentioned above, content typically belongs to a single optional content group
         and is visible when the group is ON and invisible when it is OFF. To express more
         complex visibility policies, content should declare itself not to belong directly to

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