CHAPTER 10
944
Document Interchange
10.8.3 Replacement Text
Just as alternate descriptions can be provided for images and other items that do
not translate naturally into text (as described in the preceding section), replace-
ment text can be specified for content that does translate into text but that is rep-
resented in a nonstandard way. These nonstandard representations might
include, for example, glyphs for ligatures or custom characters, or inline graphics
corresponding to letters in an illuminated manuscript or to dropped capitals.
Replacement text can be specified for the following items:
•
A structure element (see Section 10.6.1, “Structure Hierarchy”), by means of
the optional
ActualText
entry
(PDF 1.4)
of the structure element dictionary.
•
(PDF 1.5)
A marked-content sequence (see Section 10.5, “Marked Content”),
through an
ActualText
entry in a property list attached to the marked-content
sequence with a
Span
tag.
The
ActualText
value is not a description but a replacement for the content, pro-
viding text that is equivalent to what a reader with sight would see when viewing
the content. In contrast to the value of
Alt
, which is considered to be a word or
phrase substitution, the value of
ActualText
is considered to be a character substi-
tution for the structure element or marked-content sequence. Thus, if each of two
(or more) consecutive structure or marked-content sequences has an
ActualText
entry, they should be treated as if no word break is present between them.
The following example shows the use of replacement text to indicate the correct
character content in a case where hyphenation changes the spelling of a word (in
German, up until recent spelling reforms, the word “Drucker” when hyphenated
was rendered as “Druk-” and “ker”).
Example 10.24
(Dru) Tj
/Span
<</Actual Text (c) >>
BDC
(k-) Tj
EMC
(ker) '
Like alternate descriptions (and other text strings), replacement text, if encoded
in Unicode, may include an escape sequence for indicating the language of the
text, overriding the prevailing
Lang
entry (see Section , “Text String Type”).