CHAPTER 3
166
Syntax
3.8.6 Number Trees
A
number tree
is similar to a name tree (see Section 3.8.5, “Name Trees”), except
that its keys are integers instead of strings and are sorted in ascending numerical
order. The entries in the leaf (or root) nodes containing the key-value pairs are
named
Nums
instead of
Names
as in a name tree. Table 3.34 shows the entries in a
number tree’s node dictionaries.
TABLE 3.34 Entries in a number tree node dictionary
KEY
TYPE
VALUE
Kids
array
(Root and intermediate nodes only; required in intermediate nodes; present in the root
node if and only if
Nums
is not present)
An array of indirect references to the immediate
children of this node. The children may be intermediate or leaf nodes.
(Root and leaf nodes only; required in leaf nodes; present in the root node if and only if
Kids
is not present)
An array of the form
[
key
1
value
1
key
2
value
2
…
key
n
value
n
]
Nums
array
where each
key
i
is an integer and the corresponding
value
i
is the object associated with
that key. The keys are sorted in numerical order, analogously to the arrangement of keys
in a name tree as described in Section 3.8.5, “Name Trees.”
Limits
array
(Intermediate and leaf nodes only; required)
An array of two integers, specifying the
(numerically) least and greatest keys included in the
Nums
array of a leaf node or in the
Nums
arrays of any leaf nodes that are descendants of an intermediate node.
3.9 Functions
PDF is not a programming language, and a PDF file is not a program. However,
PDF does provide several types of
function objects (PDF 1.2)
that represent
parameterized classes of functions, including mathematical formulas and
sampled representations with arbitrary resolution. Functions are used in various
ways in PDF, including device-dependent rasterization information for high-
quality printing (halftone spot functions and transfer functions), color transform
functions for certain color spaces, and specification of colors as a function of
position for smooth shadings.