CHAPTER 10
936
Document Interchange
tion, either through a screen reader or by some more direct invocation of a text-
to-speech engine, PDF supports the following features:
•
Specifying the natural language used for text in a PDF document—for example,
as English or Spanish, or used to hide or reveal optional content (see Section
•
Providing textual descriptions for images or other items that do not translate
naturally into text (Section 10.8.2, “Alternate Descriptions”), or replacement
text for content that does translate into text but is represented in a nonstandard
way (such as with a ligature or illuminated character; see Section 10.8.3,
•
Specifying the expansion of abbreviations or acronyms (Section 10.8.4, “Ex-
The core of this support lies in the ability to determine the logical order of con-
tent in a PDF document, independently of the content’s appearance or layout,
through logical structure and Tagged PDF, as described under “Page Content
ument for presentation to users with disabilities by traversing the structure hier-
archy and presenting the contents of each node. For this reason, producers of
PDF files must ensure that all information in a document is reachable by means
of the structure hierarchy, and they are strongly encouraged to use the facilities
described in this section.
Note:
Text can be extracted from Tagged PDF documents and examined or reused
for purposes other than accessibility; see Section 10.7, “Tagged PDF.”
Additional guidelines for accessibility support of content published on the Web
can be found in the W3C document
Web Content Accessibility Guidelines
and the
documents it points to (see the Bibliography).
10.8.1 Natural Language Specification
Natural language can be specified for text in a document or for optional content.
The natural language used for text in a document is determined in a hierarchical
fashion, based on whether an optional
Lang
entry
(PDF 1.4)
is present in any of
several possible locations. At the highest level, the document’s default language
(which applies to both text strings and text within content streams) can be speci-