Previous Next

                                                       942
       CHAPTER 10                                                            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
       9.12 for examples of its use.) The array contains pairs of strings:

       • 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.

Previous Next