CHAPTER 4
374
Graphics
Optional Content in XObjects and Annotations
In addition to marked content within content streams, form XObjects and image
XObjects (see Section 4.7, “External Objects”) and annotations (see Section 8.4,
OC
entry, which is an optional content group or
an optional content membership dictionary.
A form or image XObject's visibility is determined by the state of the group or
those of the groups referenced by the membership dictionary in conjunction with
its
P
(or
VE
) entry, along with the current visibility state in the context in which
the XObject is invoked (that is, whether objects are visible in the contents stream
at the place where the
Do
operation occurred).
Annotations have various flags controlling on-screen and print visibility (see Sec-
OC
entry, it is visible
for screen or print only if the flags have the appropriate settings and the group or
membership dictionary indicates it is visible.
4.10.3 Configuring Optional Content
A PDF document containing optional content can specify the default states for
the optional content groups in the document and indicate which external factors
should be used to alter the states. The following sections describe the PDF struc-
tures that are used to specify this information.
•
that lists all the optional content groups in the document and their possible
configurations.
•
structures that specify initial state settings and other information about the
groups in the document.
•
groups can be affected based on external factors.