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SECTION 4.10                                                             Optional Content



Note: Although the marked-content tag must be OC, other applications of marked
content are not precluded from using OC as a tag. The marked content is considered
to be for optional content only if the tag is OC and the dictionary operand is a valid
optional content group or optional content membership dictionary.

To avoid conflict with other features that used marked content (such as logical
structure; see Section 10.6, “Logical Structure”), the following strategy is recom-
mended:
• Where content is to be tagged with optional content markers as well as other
  markers, the optional content markers should be nested inside the other
  marked content.
• Where optional content and the other markers would overlap but there is not
  strict containment, the optional content should be broken up into two or more
  BDC/EMC sections, nesting the optional content sections inside the others as
  necessary. Breaking up optional content spans does not damage the nature of
  the visibility of the content, whereas the same guarantee cannot be made for all
  other uses of marked content.

Note: Any marked content tagged for optional content that is nested inside other
marked content tagged for optional content is visible only if all the levels indicate
visibility. In other words, if the settings that apply to the outer level indicate that the
content should be hidden, the inner level is hidden regardless of its settings.

In the following example, the state of the Show Greeting optional content group
directly controls the visibility of the text string “Hello” on the page. When the
group is ON, the text is visible; when the group is OFF, the text is hidden.

Example 4.35

   % Within a content stream
   ...
   /OC /oc1 BDC                                  % Optional content follows
       BT
          /F1 1 Tf
          12 0 0 12 100 600 Tm
          (Hello) Tj
       ET
   EMC                                           % End of optional content
   ...

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