CHAPTER 3
152
Syntax
erator must immediately precede that operator. Operators do not return results, and
operands cannot be left over when an operator finishes execution.
Most operators have to do with painting graphical elements on the page or with
specifying parameters that affect subsequent painting operations. The individual
operators are described in the chapters devoted to their functions:
•
strokes, and sampled images, and that specify device-independent graphical
parameters, such as color.
•
fonts.
•
eters.
•
logical information with objects in the content stream. These operators do not
affect the rendered appearance of the content; they specify information useful
to applications that use PDF for document interchange.
Ordinarily, when an application encounters an operator in a content stream that
it does not recognize, an error occurs. (See implementation note 39 in Appendix
BX
and
EX
(PDF 1.1),
modify this behavior
(see Table 3.29). These operators must occur in pairs and may be nested. They
bracket a
compatibility section,
a portion of a content stream within which
unrecognized operators are to be ignored without error. This mechanism enables
a PDF document to use operators defined in later versions of PDF without
sacrificing compatibility with older applications. It should be used only in cases
where ignoring such newer operators is the appropriate thing to do. The
BX
and
EX
operators are not themselves part of any graphics object (see Section 4.1,
TABLE 3.29 Compatibility operators
OPERANDS
OPERATOR
DESCRIPTION
—
BX
(PDF 1.1)
Begin a compatibility section. Unrecognized operators (along with their
operands) are ignored without error until the balancing
EX
operator is encountered.
(PDF 1.1)
End a compatibility section begun by a balancing
BX
operator.
—
EX