SECTION 10.8
943
Accessibility Support
•
Any type of annotation (see Section 8.4, “Annotations”) that does not already
have a text representation, through a
Contents
entry in the annotation dic-
tionary
For annotation types that normally display text, that text (specified in the
Contents
entry of the annotation dictionary) is the natural source for vocalization
purposes. For annotation types that do not display text, a
Contents
entry
(PDF
1.4)
can optionally be included to specify an alternate description. Sound annota-
tions, which are vocalized by default and therefore need no alternate description
for that purpose, can include a
Contents
entry specifying a description to be dis-
played in a pop-up window for the benefit of users with hearing impairments.
In addition, an alternate name can be specified for an interactive form field (see
wherever the field must be identified in the user interface (such as in error or sta-
tus messages referring to the field). This alternate name, specified in the optional
TU
entry of the field dictionary, can be useful for vocalization purposes.
Alternate descriptions are text strings, which may be encoded in either
PDFDocEncoding
or Unicode character encoding. As described in Section , “Text
the text. This mechanism enables the alternate description to change from the
language specified by the prevailing
Lang
entry (as described in the preceding
section).
When applied to structure elements, the text is considered to be a word or phrase
substitution for the current element. For example, if each of two (or more) ele-
ments in a sequence has an
Alt
entry in its dictionary, they should be treated as if
a word break is present between them. The same would apply to consecutive
marked-content sequences.
Note:
The
Alt
entry in property lists can be combined with other entries, as shown in
Example 10.23
/Span << /Lang (en-us) /Alt (six-point star) >> BDC (✡) Tj EMC