SECTION 10.7
905
Tagged PDF
The strongly structured paradigm is used by some rich document models based
on XML. The weakly structured paradigm is typical of documents represented in
HTML.
Lists and tables should be organized using the specific structure types described
under “List Elements” on page 902 and “Table Elements” on page 903. Likewise,
tables of contents and indexes should be structured as described for the
TOC
and
Index
structure types under “Grouping Elements” on page 899.
Inline-Level Structure Elements
An
inline-level structure element (ILSE)
contains a portion of text or other content
having specific styling characteristics or playing a specific role in the document.
Within a paragraph or other block defined by a containing BLSE, consecutive
ILSEs—possibly intermixed with other content items that are direct children of
the parent BLSE—are laid out consecutively in the inline-progression direction
(left to right in Western writing systems). The resulting content may be broken
into multiple
lines,
which in turn are stacked in the block-progression direction.
It is possible for an ILSE in turn to contain a BLSE, which is treated as a unitary
item of layout in the inline direction. Table 10.25 lists the standard structure types
for ILSEs.
TABLE 10.25 Standard structure types for inline-level structure elements
STRUCTURE TYPE
DESCRIPTION
Span
(Span) A generic inline portion of text having no particular inherent characteristics. It can
be used, for example, to delimit a range of text with a given set of styling attributes.
Note:
Not all inline style changes need to be identified as a span. Text color and font changes
(including modifiers such as bold, italic, and small caps) need not be so marked, since these
can be derived from the PDF content (see “Font Characteristics” on page 892). However, it is
necessary to use a span to apply explicit layout attributes such as
LineHeight
,
BaselineShift
, or
TextDecorationType
(see “Layout Attributes for ILSEs” on page 926).
Note:
Marked-content sequences having the tag
Span
are also used to carry certain accessibil-
ity properties (
Alt
,
ActualText
,
Lang
, and
E
; see Section 10.8, “Accessibility Support”). Such se-
quences lack an
MCID
property and are not associated with any structure element. This use of
the
Span
marked-content tag is distinct from its use as a structure type.