CHAPTER 8
680
Interactive Features
viewer should insert one in the appearance stream (with appropriate horizontal
and vertical translation components) after the default appearance string and be-
fore the text-positioning and text-showing operators for the variable text.
To update an existing appearance stream to reflect a new field value, the viewer
application should first copy any needed resources from the document’s
DR
dic-
tionary (see Table 8.67) into the stream’s
Resources
dictionary. (If the
DR
and
Resources
dictionaries contain resources with the same name, the one already in
the
Resources
dictionary should be left intact,
not
replaced with the correspond-
ing value from the
DR
dictionary.) The viewer application should then replace the
existing contents of the appearance stream from
/Tx BMC
to the matching
EMC
with the corresponding new contents as shown in Example 8.14. (If the existing
appearance stream contains no marked content with tag
Tx
, the new contents
should be appended to the end of the original stream.) Also see implementation
Rich Text Strings
Beginning with PDF 1.5, the text contents of variable text form fields, as well as
markup annotations, can include formatting (style) information. These
rich text
strings
are fully-formed XML documents that conform to the rich text conven-
tions specified for the XML Forms Architecture (XFA) specification, which is it-
self a subset of the XHTML 1.0 specification, augmented with a restricted set of
CSS2 style attributes (see the Bibliography for references to all these standards).
<body>
element is the root element; its required attributes are listed in Table 8.73.
Other elements (
<p>
and
<span>
) contain enclosed text that may take style at-
tributes, which are listed in Table 8.74. These style attributes are CSS inline style
property declarations of the form
name:value
, with each declaration separated by
a semicolon, as illustrated in Example 8.15 on page 684.
In PDF 1.6, PDF supports the rich text elements and attributes specified in the
XML Forms Architecture (XFA) Specification, 2.2
(see Bibliography). These rich
text elements and attributes are a superset of those described in Table 8.72, Table
tributes specified in the
XML Forms Architecture (XFA) Specification, 2.4
(see Bib-
attributes; however, XFA 2.4 expands the range of supported character codes.