CHAPTER 10
868
Document Interchange
EMC
…
endstream
endobj
% End of marked-content sequence
PDF Objects as Content Items
When a structure element’s content includes an entire PDF object, such as an
XObject or an annotation, that is associated with a page but not directly included
in the page’s content stream, the object is identified in the structure element’s
K
entry by an
object reference dictionary
(see Table 10.12). Note that this form of
reference is used only for entire objects. If the referenced content forms only part
of the object’s content stream, it is instead handled as a marked-content sequence,
as described in the preceding section.
TABLE 10.12 Entries in an object reference dictionary
KEY
TYPE
VALUE
Type
name
dictionary
(Required)
The type of PDF object that this dictionary describes; must be
OBJR
for an
object reference.
(Optional; must be an indirect reference)
The page object representing the page on
which the object is rendered. This entry overrides any
Pg
entry in the structure ele-
ment containing the object reference; it is required if the structure element has no such
entry.
(Required; must be an indirect reference)
The referenced object.
Pg
Obj
(any)
Note:
If the referenced object is rendered on multiple pages, each rendering requires
a separate object reference. However, if it is rendered multiple times on the same
page, just a single object reference suffices to identify all of them. (If it is important
to distinguish between multiple renditions of the same XObject on the same page,
they should be accessed by means of marked-content sequences enclosing particular
invocations of the
Do
operator rather than through object references.)
Finding Structure Elements from Content Items
Because a stream cannot contain object references, there is no way for content
items that are marked-content sequences to refer directly back to their parent
structure elements (the ones to which they belong as content items). Instead, a