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                                                      166
           CHAPTER 3                                                                             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.

Nums        array     (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
                         [ key1 value1 key2 value2 … keyn valuen ]

                      where each keyi is an integer and the corresponding valuei 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.

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