When to use Alternative, Actual, or Expansion Text (Desktop and Advanced Editor)

Overview

Accessible PDFs provide several mechanisms for supplying information to assistive technologies that may not be available from the visible content alone. Three of the most common are Alternate Text (Alt Text), Actual Text, and Expansion Text. While they all provide additional information to users of assistive technology, they serve different purposes. 

Alternate Text (Alt Text)

Alternate Text, commonly referred to as Alt Text, provides a text description for non-text content such as images, charts, diagrams, illustrations, and logos. When a screen reader encounters a figure, it announces the Alt Text instead of attempting to interpret the visual content. Alt Text allows users who cannot see the image to understand its purpose or meaning within the document

Actual Text

Actual Text provides a replacement for the visible content itself. When Actual Text is present, assistive technologies and copy-and-paste operations use the Actual Text value instead of the displayed characters. This is particularly useful for symbols, mathematical notation, special characters, ligatures, decorative glyphs, or situations where the visible text does not accurately represent the intended accessible content

Expansion Text

Expansion Text provides the full meaning of an abbreviation, acronym, or initialism. It allows assistive technologies to present the expanded form of a shortened term, helping users understand abbreviations that might otherwise be unclear.

Prerequisites 

• Alternative text: Alternative text describes the image or tells the listener the relevant content that is being shown visually in images, charts, diagrams, logos, etc.  
• Actual text:  Use this option when you need to replace visible content with accessible text.  Examples include drop caps, symbols, equations, and special characters.
• Expansion text:  Used to provide the full form of abbreviations and acronyms.

Steps to Follow

The Properties panel (for any tag) includes options for adding any of the three text options.   With that said, most of the time figure tags will need alternative text to describe them.  Actual text can be applied to figure tags, but it can also be applied to span tags or tags holding symbols or other special characters that are not graphical elements (paths, Xobjects, etc).  Lastly, expansion text is commonly applied to span tags surrounding abbreviations or acronyms.

Common Problems

Do not put information in more than one field (Alternative and Actual, for example).  Some screen readers will only read the content in one of the boxes and then proceed to the next tag in the tree.  If there is information in more than one field, it may be ignored.

Frequently Asked Questions

How does a screen reader read alternative, actual, or expansion text of a tag?

When a screen reader “lands on” a tag in the Tags tree, it refers to the properties of that tag to see if there is alternative, actual, or expansion text provided.  If there is, it will read the text and move on to the next tag in the tree.

What are best practices in terms of using expansion text for abbreviations and acronyms?

While the standards do not explicitly state that expansion text must be used, it is recommended that any abbreviation or acronym that is not already made clear to a reader in the text of the PDF should be identified by expansion text the first time it is used in the document.  It is not recommended to add expansion text to every occurrence of the abbreviation or acronym.
 

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