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      CHAPTER 8                                                        Interactive Features



 8.3 Page-Level Navigation
      This section describes PDF facilities that enable the user to navigate from page to
      page within a document:

      • Page labels for numbering or otherwise identifying individual pages (see Sec-
        tion 8.3.1)
      • Article threads, which chain together items of content within the document that
        are logically connected but not physically sequential (see Section 8.3.2)
      • Presentations that display the document in the form of a slide show, advancing
        from one page to the next either automatically or under user control (see Sec-
        tion 8.3.3)

      For another important form of page-level navigation, see “Link Annotations” on
      page 622.


8.3.1 Page Labels

      Each page in a PDF document is identified by an integer page index that expresses
      the page’s relative position within the document. In addition, a document may
      optionally define page labels (PDF 1.3) to identify each page visually on the screen
      or in print. Page labels and page indices need not coincide: the indices are fixed,
      running consecutively through the document starting from 0 for the first page,
      but the labels can be specified in any way that is appropriate for the particular
      document. For example, if the document begins with 12 pages of front matter
      numbered in roman numerals and the remainder of the document is numbered
      in arabic, the first page would have a page index of 0 and a page label of i, the
      twelfth page would have index 11 and label xii, and the thirteenth page would
      have index 12 and label 1.

      For purposes of page labeling, a document can be divided into labeling ranges,
      each of which is a series of consecutive pages using the same numbering system.
      Pages within a range are numbered sequentially in ascending order. A page’s label
      consists of a numeric portion based on its position within its labeling range,
      optionally preceded by a label prefix denoting the range itself. For example, the
      pages in an appendix might be labeled with decimal numeric portions prefixed
      with the string A−; the resulting page labels would be A−1, A−2, and so on.

      A document’s labeling ranges are defined by the PageLabels entry in the docu-
      ment catalog (see Section 3.6.1, “Document Catalog”). The value of this entry is a

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