SECTION 10.7
913
Tagged PDF
10.7.4 Standard Structure Attributes
In addition to the standard structure types, Tagged PDF defines standard layout
and styling attributes for structure elements of those types. These attributes en-
able predictable formatting to be applied during operations such as reflow and
export of PDF content to other document formats.
As discussed in Section 10.6.4, “Structure Attributes,” attributes are defined in
attribute objects,
which are dictionaries or streams attached to a structure element
in either of two ways:
•
The
A
entry in the structure element dictionary identifies an attribute object or
an array of such objects.
•
The
C
entry in the structure element dictionary gives the name of an
attribute
class
or an array of such names. The class name is in turn looked up in the
class
map,
a dictionary identified by the
ClassMap
entry in the structure tree root,
yielding an attribute object or array of objects corresponding to the class.
In addition to the standard structure attributes described below, there are several
other optional entries—
Lang
,
Alt
,
ActualText
, and
E
—that are described in Sec-
They appear in the following places in a PDF file (rather than in attribute dictio-
naries):
•
As entries in the structure element dictionary (see Table 10.10 on page 858)
•
As entries in property lists attached to marked-content sequences with a
Span
tag (see Section 10.5, “Marked Content”)
Standard Attribute Owners
Each attribute object has an
owner,
specified by the object’s
O
entry, which deter-
mines the interpretation of the attributes defined in the object’s dictionary. Multi-
ple owners may define like-named attributes with different value types or
interpretations. Tagged PDF defines a set of standard attribute owners, shown in