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       CHAPTER 10                                                      Document Interchange



       (such as hyphenation points within a word), and the remaining fragment is car-
       ried over to the next line.

       Note: Certain values of an element’s Placement attribute remove the element from
       the normal stacking or packing process and allow it instead to float to a specified
       edge of the enclosing reference area or parent BLSE; see “General Layout Attributes”
       on page 917 for further discussion.

       Two enclosing rectangles are associated with each BLSE and ILSE (including
       direct content items that are treated implicitly as ILSEs):

       • The content rectangle is derived from the shape of the enclosed content and
         defines the bounds used for the layout of any included child elements.
       • The allocation rectangle includes any additional borders or spacing surround-
         ing the element, affecting how it is positioned with respect to adjacent elements
         and the enclosing content rectangle or reference area.

       The definitions of these rectangles are determined by layout attributes associated
       with the structure element; see “Content and Allocation Rectangles” on page 930
       for further discussion.


10.7.3 Standard Structure Types

       Tagged PDF’s standard structure types characterize the role of a content element
       within the document and, in conjunction with the standard structure attributes
       (described in Section 10.7.4, “Standard Structure Attributes”), how that content is
       laid out on the page. As discussed in Section 10.6.2, “Structure Types,” the struc-
       ture type of a logical structure element is specified by the S entry in its structure
       element dictionary. To be considered a standard structure type, this value must be
       either:
       • One of the standard structure type names described below.
       • An arbitrary name that is mapped to one of the standard names by the docu-
         ment’s role map (see Section 10.6.2, “Structure Types”), possibly through multi-
         ple levels of mapping.

       Note: Beginning with PDF 1.5, an element name is always mapped to its corre-
       sponding name in the role map, if there is one, even if the original name is one of the
       standard types. This is done to allow the element, for example, to represent a tag
       with the same name as a standard role, even though its use differs from the standard
       role.

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