The ISO (International Organization for Standardization) published ISO 14289 – the PDF accessibility standard otherwise known as PDF/UA – in 2008.  Because, however, PDF accessibility can be a confusing topic, it seems like a good idea to provide non-technical definitions of some of the key terms users, developers, and policy-makers will encounter as they learn more about PDF accessibility.

This post is intended to make some of the more common technical language of PDF accessibility itself accessible. If you seek further clarification, please contact us by email at

Add Tags

A feature in Adobe’s Acrobat Professional software, “Add Tags,” creates a Tags (Structure) Tree and attempts to create tags in a logical reading order and with correct semantics. While Add Tags can work fairly well on very simple documents, the potential for errors increases with document complexity. While “Add Tags” is the name of a specific feature in Adobe Acrobat Professional, other PDF creation applications like Microsoft Office, Open Office, and Adobe InDesign are also capable of creating tagged PDF files.


This refers to items on a page, or in a document, that don’t really need to be read out loud when someone is using assistive technology to read a document.  While wholly distinct from real content, artifacts may provide relevant information to some users – printed page numbers, for example.  Other examples of artifacted content – things that by themselves do not convey relevant information – include the borders around cells in a data table, running headers and/or footers (that repeat on multiple pages), or decorative images.  PDF/UA specifies that conforming software be capable of reporting artifacts to the user.


A suite of tools for the creation, verification, correction, and management of accessible PDF files, CommonLook is a brand of NetCentric Technologies, the company that owns the website you are reading right now.

Content Panel

Adobe’s Acrobat Professional includes a “Content Panel” that displays all of the content (text images, etc.), page by page, in a PDF.  Contrary to popular belief, it does not have anything to do with the reading order of the PDF.

Physical View

This refers to how the content is displayed visibly on the page.  The Physical View strongly influences how someone looking at a document will read it.  Generally speaking, in most languages, we’d read the page from left to right and from the top to the bottom.

Reading Order (Logical Reading Order)

This is the order in which assistive technologies, like screen readers or refreshable braille displays, present the content in a PDF.  This order is determined by the tags in the Tags (Structure) Tree.  Ideally, the Reading Order closely (or identically) matches the Physical View so that someone using assistive technology gets the same information in the same sequence as someone who is visually looking at a document.  A key component of PDF accessibility, the Reading Order is determined by the tags in the Tags (Structure) Tree.

Real Content

This refers to text, images, and other content required to comprehend the document. Page content that isn’t necessary for understanding the document should be marked as an artifact.


Semantics define the purpose of content in terms of its relationship to other content.  For example, headings are often used to define sections of a document for organizational purposes – like chapters in a book.   Lists, whether ordered (with numbers) or unordered (with bullets) will have a certain number of List Items.  Data tables will be constructed with a number of rows, each row containing headers (column or row headers) and/or data.  PDF/UA requires that the most “semantically appropriate” tag be used for the content.  This means, for example, that if a list appears visually on a page it should be tagged as a list in the Tags (Structure) Tree.

Tagged PDF

A “tagged PDF” includes elements that organize (establish the reading order) and characterize (semantics) the PDF page’s content for reuse (for example, by assistive technology).

Tags (Structure) Tree

Every tagged PDF includes a Tags (Structure) Tree containing tags that define the reading order and establishes the semantics of content in the document.


These are the “branches” and “leaves” of the Tags Tree. In a PDF, tags are the fundamental mechanism by which content is made accessible.

Tags Panel

Adobe Acrobat Professional includes a “Tags Panel” which allows the user to verify and manage the reading order of the PDF’s real content.

Touch Up Reading Order Tool (TUROT)

Adobe Acrobat Professional includes this tool to facilitate modification of the tagging and reading order on a PDF page.  While useful in some circumstances (typically with simple documents), there are faster, easier, and more efficient ways to fix accessibility issues in PDFs.  (CommonLook PDF GlobalAccess!)


This refers to the layering of content on the PDF’s page.  Determined by the Z-Order and Content Panels in Acrobat, text and images on a page may be “behind” or “in front of” other objects, such as when text is overlaid on a photograph. If thinking about X and Y axes for horizontal and vertical layout on a page, the Z axis, then, would be “what is on top of what.”

Z-Order Panel

Adobe’s Acrobat Professional includes a “Z-Order Panel” that works in conjunction with the Content Panel to determine how content is displayed on the page.  While there is some connection between the Z-Order Panel and the Tags Panel, contrary to popular belief, the Z-Order Panel does not have anything to do with the reading order of the PDF.  The reading order is derived 100% from the Tags in the Tags (Structure) Tree.