Adobe ACROBAT 3D, Manual, Page: 366 / 822

Understanding how tags affect accessibility
To make sure that your Adobe PDF documents can be accessed reliably, you must add
tags to them. Tagging adds an underlying organizational structure, or logical structure
tree, to the document. The logical structure tree refers to the organization of the
document's content, such as title page, chapters, sections, and subsections. It can indicate
the precise reading order and improve navigation--particularly for longer, more complex
documents--without changing the appearance of the PDF document.
For people who are not able to see or decode the visual appearance of documents,
assistive technology can access the content of the document reliably by using the logical
structure tree. Most assistive technology depends on this structure to convey the meaning
of content and images in an alternative format, such as sound. In an untagged document,
no such structure exists, and Acrobat must infer a structure based on the reading order
choices in the preferences. This method is unreliable and often results in page items read
in the wrong order or not read at all.
Often, Acrobat tags PDF documents when you create them. To determine if a PDF
document contains tags, check the Document Properties. (See
Tagging Adobe PDF
documents for accessibility .)
Note: The logical structure tree appears on the Tags tab in the navigation pane and shows
document content as page elements nested at various levels.
Logical structure tree on the Tags tab
Note: PDF tags can be compared to HTML tags and XML tags, although there are
differences. To learn more about basic tagging concepts, see any of the many references
and textbooks available in bookstores, libraries, and on the web.