CHAPTER 10
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Document Interchange
KEY
TYPE
VALUE
Lang
text string
(Optional; PDF 1.4)
A
language identifier
specifying the natural language
for all text in the structure element except where overridden by language
specifications for nested structure elements or marked content (see Sec-
language (if any) specified in the document catalog applies.
(Optional)
An alternate description of the structure element and its
children in human-readable form, which is useful when extracting the
document’s contents in support of accessibility to users with disabilities
or for other purposes (see Section 10.8.2, “Alternate Descriptions”).
(Optional; PDF 1.5)
The expanded form of an abbreviation.
(Optional; PDF 1.4)
Text that is an exact replacement for the structure
element and its children. This replacement text (which should apply to
as small a piece of content as possible) is useful when extracting the doc-
ument’s contents in support of accessibility to users with disabilities or
for other purposes (see Section 10.8.3, “Replacement Text”).
Alt
text string
E
ActualText
text string
text string
10.6.2 Structure Types
Every structure element has a
structure type,
a name object that identifies the
nature of the structure element and its role within the document (such as a chap-
ter, paragraph, or footnote). To facilitate the interchange of content among PDF
applications, Adobe has defined a set of standard structure types; see Section
however, and may use any names for their structure types.
Where names other than the standard ones are used, a
role map
may be provided
in the structure tree root, mapping the structure types used in the document to
their nearest equivalents in the standard set. For example, a structure type named
Section
used in the document might be mapped to the standard type
Sect
. The
equivalence need not be exact; the role map merely indicates an approximate
analogy between types, allowing applications other than the one creating a docu-
ment to handle its nonstandard structure elements in a reasonable way.
Note:
The same structure type may occur as both a key and a value in the role map,
and circular chains of association are explicitly permitted. A single role map can
thus define a bidirectional mapping. An application using the role map should fol-