CHAPTER 8
594
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-
•
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-
For another important form of page-level navigation, see “Link Annotations” on
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