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SECTION 10.8                                                        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
Section 8.6, “Interactive Forms”), to be used in place of the actual field name
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
String Type,” Unicode defines an escape sequence for indicating the language of
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.

Example 10.23

   /Span << /Lang (en-us) /Alt (six-point star) >> BDC (✡) Tj EMC

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