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SECTION 3.6 Document Structure
Inheritance of Page Attributes
Some of the page attributes shown in Table 3.27 are designated as inheritable. If
such an attribute is omitted from a page object, its value is inherited from an
ancestor node in the page tree. If the attribute is a required one, a value must be
supplied in an ancestor node. If the attribute is optional and no inherited value is
specified, the default value is used.
An attribute can thus be defined once for a whole set of pages by specifying it in
an intermediate page tree node and arranging the pages that share the attribute as
descendants of that node. For example, a document might specify the same
media box for all of its pages by including a MediaBox entry in the root node of
the page tree. If necessary, an individual page object could override this inherited
value with a MediaBox entry of its own.
Note: In a document conforming to the Linearized PDF organization (see Appen-
dix F), all page attributes must be specified explicitly as entries in the page dictio-
naries to which they apply; they may not be inherited from an ancestor node.
Figure 3.6 illustrates the inheritance of attributes. In the page tree shown, pages 1,
2, and 4 are rotated clockwise by 90 degrees, page 3 by 270 degrees, page 6 by 180
degrees, and pages 5 and 7 not at all (0 degrees).
Pages
Pages Pages Pages
/Rotate 90 /Rotate 180
Page Page Pages Page Page Page
/Rotate 0
Page 1 Page 2 Page 5 Page 6 Page 7
Page Page
/Rotate 270 /Rotate 90
Page 3 Page 4
FIGURE 3.6 Inheritance of attributes
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