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           CHAPTER 8                                                                 Interactive Features



KEY       TYPE          VALUE

P         text string   (Optional) The label prefix for page labels in this range.

St        integer       (Optional) The value of the numeric portion for the first page label in the range. Sub-
                        sequent pages are numbered sequentially from this value, which must be greater than or
                        equal to 1. Default value: 1.


     8.3.2 Articles

           Some types of documents may contain sequences of content items that are logi-
           cally connected but not physically sequential. For example, a news story may be-
           gin on the first page of a newsletter and run over onto one or more
           nonconsecutive interior pages. To represent such sequences of physically discon-
           tiguous but logically related items, a PDF document may define one or more arti-
           cles (PDF 1.1). The sequential flow of an article is defined by an article thread; the
           individual content items that make up the article are called beads on the thread.
           PDF viewer applications can provide navigation facilities to allow the user to fol-
           low a thread from one bead to the next.

           The optional Threads entry in the document catalog (see Section 3.6.1, “Docu-
           ment Catalog”) holds an array of thread dictionaries (Table 8.11) defining the
           document’s articles. Each individual bead within a thread is represented by a bead
           dictionary (Table 8.12). The thread dictionary’s F entry points to the first bead in
           the thread; the beads are chained together sequentially in a doubly linked list
           through their N (next) and V (previous) entries. In addition, for each page on
           which article beads appear, the page object (see “Page Objects” on page 144)
           should contain a B entry whose value is an array of indirect references to the
           beads on the page, in drawing order.

                                     TABLE 8.11 Entries in a thread dictionary
KEY        TYPE              VALUE

Type       name              (Optional) The type of PDF object that this dictionary describes; if present, must be
                             Thread for a thread dictionary.

F          dictionary        (Required; must be an indirect reference) The first bead in the thread.

I          dictionary        (Optional) A thread information dictionary containing information about the thread,
                             such as its title, author, and creation date. The contents of this dictionary are similar
                             to those of the document information dictionary (see Section 10.2.1, “Document In-
                             formation Dictionary”).

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