CHAPTER 4
362
Graphics
jects can use the proxy in place of the imported content if the latter is unavailable.
An application may also provide a user interface to allow editing and updating of
imported content links.
The imported content consists of a single, complete PDF page in the target docu-
ment. It is designated by a
reference dictionary,
which in turn is the value of the
Ref
entry in the reference XObject’s form dictionary (see Section 4.9.1, “Form
Ref
entry distinguishes reference XObjects
from other types of form XObjects. Table 4.47 shows the contents of the reference
dictionary.
TABLE 4.47 Entries in a reference dictionary
KEY
TYPE
VALUE
F
Page
file specification
integer or
text string
(Required)
The file containing the target document.
(Required)
A page index or page label (see Section 8.3.1, “Page Labels”) iden-
tifying the page of the target document containing the content to be
imported. Note that the reference is a weak one and can be inadvertently in-
validated if the referenced page is changed or replaced in the target document
after the reference is created.
(Optional)
An array of two byte strings constituting a file identifier (see Sec-
use of this entry improves an application’s chances of finding the intended file
and allows it to warn the user if the file has changed since the reference was
created.
ID
array
When the imported content replaces the proxy, it is transformed according to the
proxy object’s transformation matrix and clipped to the boundaries of its bound-
ing box, as specified by the
Matrix
and
BBox
entries in the proxy’s form dictionary
(see Section 4.9.1, “Form Dictionaries”). The combination of the proxy object’s
matrix and bounding box thus implicitly defines the bounding box of the import-
ed page. This bounding box typically coincides with the imported page’s crop box
or art box (see Section 10.10.1, “Page Boundaries”), but it is not required to corre-
spond to any of the defined page boundaries. If the proxy object’s form dictionary
contains a
Group
entry, the specified group attributes apply to the imported page
as well, which allows the imported page to be treated as a group without further
modification.