CHAPTER 10
942
Document Interchange
Multi-language Text Arrays
A
multi-language text array (PDF 1.5)
allows multiple text strings to be specified,
each in association with a language identifier. (See the
Alt
entry in Tables 9.9 and
•
The first string in each pair is an ASCII string language identifier. A given lan-
guage identifier may not appear more than once in the array; any unrecognized
language identifier should be ignored. An empty string specifies default text to
be used when no matching language identifier is found in the array.
•
The second byte string is text associated with the language.
Example 10.22
[ (en-US) (My vacation) (fr) (mes vacances) ( ) (default text) ]
When a consumer application searches a multi-language text array to find text for
a given language, it should look for an exact (though case-insensitive) match be-
tween the given language’s identifier and the language identifiers in the array. If
no exact match is found, prefix matching is attempted in increasing array order: a
match is declared if the given identifier is a leading, case-insensitive, substring of
an identifier in the array, and the first post-substring character in the array iden-
tifier is a hyphen. For example, given identifier
en
matches array identifier
en-US
,
but given identifier
en-US
matches neither
en
nor
en-GB
. If no exact or prefix
match can be found, the default text (if any) should be used.
10.8.2 Alternate Descriptions
PDF documents can be enhanced by providing alternate descriptions for images,
formulas, or other items that do not translate naturally into text. Alternate de-
scriptions are human-readable text that could, for example, be vocalized by a
text-to-speech engine for the benefit of users with visual impairments.
An alternate description can be specified for the following items:
•
A structure element (see Section 10.6.1, “Structure Hierarchy”), through an
Alt
entry in the structure element dictionary
•
(PDF 1.5)
A marked-content sequence (see Section 10.5, “Marked Content”),
through an
Alt
entry in a property list attached to the marked-content sequence
with a
Span
tag.