CHAPTER 10
852
Document Interchange
10.5.1 Property Lists
The marked-content operators
DP
and
BDC
associate a
property list
with a
marked-content element within a content stream. The property list is a dictionary
containing private information meaningful to the program (application or plug-
in extension) creating the marked content. It is suggested that programs use the
dictionary entries in a consistent way; for example, the values associated with a
given key should always be of the same type (or small set of types).
If all of the values in a property list dictionary are direct objects, the dictionary
may be written inline in the content stream as a direct object. If any of the values
are indirect references to objects outside the content stream, the property list
dictionary must instead be defined as a named resource in the
Properties
sub-
dictionary of the current resource dictionary (see Section 3.7.2, “Resource Dic-
properties
operand of the
DP
or
BDC
operator.
10.5.2 Marked Content and Clipping
Some PDF path and text objects are defined purely for their effect on the current
clipping path, without the objects actually being painted on the page. This occurs
when a path object is defined using the operator sequence
W n
or
W* n
(see
rendering mode 7 (see Section 5.2.5, “Text Rendering Mode”). Such clipped,
unpainted path or text objects are called
clipping objects.
When a clipping object
falls within a marked-content sequence, it is not considered part of the sequence
unless the entire sequence consists only of clipping objects. In Example 10.2, for
instance, the marked-content sequence tagged
Clip
includes the text string
( Clip me )
but not the rectangular path that defines the clipping boundary.
Example 10.2
/Clip BMC
100 100 10 10 re W n
( Clip me ) Tj
EMC
% Clipping path
% Object to be clipped
Only when a marked-content sequence consists entirely of clipping objects are
the clipping objects considered part of the sequence. In this case, the sequence is
known as a
marked clipping sequence.
Such sequences may be nested. In Example