SECTION 10.8
937
Accessibility Support
fied by a
Lang
entry in the document catalog (see Section 3.6.1, “Document Cat-
•
Structure elements of any type (see Section 10.6.1, “Structure Hierarchy”),
through a
Lang
entry in the structure element dictionary.
•
Marked-content sequences that are not in the structure hierarchy (see Section
Lang
entry in a property list attached to the
marked-content sequence with a
Span
tag. (Although
Span
is also a standard
structure type, as described under “Inline-Level Structure Elements” on page
The natural language used for optional content allows content to be hidden or re-
vealed, based on the
Lang
entry (PDF 1.5) in the
Language
dictionary of an op-
tional content usage dictionary.
The following sections provide details on the value of the
Lang
entry and the
hierarchical manner in which the language for text in a document is determined.
Note:
Text strings encoded in Unicode may include an escape sequence or language
tag indicating the language of the text and overriding the prevailing
Lang
entry (see
Language Identifiers
Certain language-related dictionary entries are text strings that specify
language
identifiers.
Such text strings appear as
Lang
entries in the following structures or
dictionaries:
•
Document catalog, structure element dictionary, or property list
•
Optional content usage dictionary’s Language dictionary, although the hierar-
chical issues described in “Language Specification Hierarchy,” below do not ap-
ply to this entry
A language identifier can either be the empty text string, to indicate that the lan-
guage is unknown, or a
Language-Tag
as defined in RFC 3066,
Tags for the Identi-
fication of Languages.
This section provides an informal summary of RFC 3066.
This syntax, which is summarized below, is also used to identify languages in
XML, according to the W3C document
Extensible Markup Language (XML) 1.1;
see the Bibliography for more information about these documents. An empty
string indicates that the language is unknown.