SECTION 8.2
585
Document-Level Navigation
items by clicking them with the mouse. When an item is open, its immediate chil-
dren in the hierarchy become visible on the screen; each child may in turn be
open or closed, selectively revealing or hiding further parts of the hierarchy.
When an item is closed, all of its descendants in the hierarchy are hidden. Click-
ing the text of any visible item
activates
the item, causing the viewer application to
jump to a destination or trigger an action associated with the item.
The root of a document’s outline hierarchy is an
outline dictionary
specified by
the
Outlines
entry in the document catalog (see Section 3.6.1, “Document Cata-
within the hierarchy is defined by an
outline item dictionary
items at each level of the hierarchy form a linked list, chained together through
their
Prev
and
Next
entries and accessed through the
First
and
Last
entries in the
parent item (or in the outline dictionary in the case of top-level items). When dis-
played on the screen, the items at a given level appear in the order in which they
occur in the linked list. (See also implementation note 74 in Appendix H.)
TABLE 8.3 Entries in the outline dictionary
KEY
TYPE
VALUE
Type
name
dictionary
(Optional)
The type of PDF object that this dictionary describes; if present,
must be
Outlines
for an outline dictionary.
(Required if there are any open or closed outline entries; must be an indirect ref-
erence)
An outline item dictionary representing the first top-level item in the
outline.
(Required if there are any open or closed outline entries; must be an indirect ref-
erence)
An outline item dictionary representing the last top-level item in the
outline.
(Required if the document has any open outline entries)
The total number of
open items at all levels of the outline. This entry should be omitted if there
are no open outline items.
First
Last
dictionary
Count
integer
TABLE 8.4 Entries in an outline item dictionary
KEY
TYPE
VALUE
Title
Parent
text string
dictionary
(Required)
The text to be displayed on the screen for this item.
(Required; must be an indirect reference)
The parent of this item in the outline
hierarchy. The parent of a top-level item is the outline dictionary itself.