Understanding Text Spacing


The intent of this Success Criterion is to help ensure that people with disabilities who override spacing can read text. It allows for a buffer. Increased spacing between lines, words, and letters has benefits for people who override author settings via user stylesheet, bookmarklet, extension, or application. They may need to change font family (e.g. to a wider one) than the author has set to effectively read text. They may increase spacing between lines, words, and letters to effectively read text. Line spacing also helps with tracking. Tracking is following along lines of text, including getting from the end of one line to the beginning of the next line.

The grounds for this SC are based on research. The metrics chosen as measures are based on the McLeish study. She ran from .04 to .25 em tests. McLeish found an increasing curve in reading speed of actual materials up to .25, but it started to flatten at .20. Previous studies that reported no improvement started at .5em. Right at the flat point. Wayne E. Dick, Ph.D. analyzed the McLeish study and translated from points. Dr. Dick recommended the metrics that the Working Group adopted.

The following images show examples of failures when authors do not take into consideration that users may override spacing to the metrics specified in this Success Criterion.

Text Cut Off

The bottom portion of the words "Your Needs" is cut off in a heading making that text unreadable in Figure 1. It should read "We Provide a Mobile Application Service to Meet Your Needs."

Figure 1: Vertical text cut off is a failure.
Heading text truncated vertically.

In Figure 2 the last portion of text is cut off in 3 side-by-side headings. The 1st heading should read "A cog in the wheel." But it reads "A cog in the whe". Only half of the second "e" is visible and the letter "l" is completely missing. The 2nd heading should read "A penny for your thoughts". But it reads "A penny for your". The 3rd should read "Back to the drawing board." But it reads "Back to the drawi".

Figure 2: Horizontal text cut off is a failure.
3 side-by-side headings with truncated text.

Text Overlap

In Figure 3 the last 3 words "Groups and Programs" of the heading "Technologists Seeking Input from Groups and Programs" overlap the following sentence. That sentence should read, "You are invited to share ideas and areas of interest related to the integration of technology from a group or program perspective." But the words "You are invited to share ideas" are obscured and unreadable.

Figure 3: Overlapping text is a failure.
Heading text overlaps part of paragraph text.

Fixed Text

Text fails the SC when it is fixed and not able to be overridden to the Success Criterion's metrics.

Text that allows for overriding to the metrics passes. Line height must be able to adapt to 1.5 times the font size. Letter spacing must be able to adapt to 0.12 times the font size. Word spacing must be able to adapt to 0.16 times the font size. Spacing underneath paragraphs must be able to adapt to 2 times the font size.

Figure 4: Absolutely fixed text is a failure. Adaptable text passes.
Spacing Fail/Pass side-by-side comparison

This SC does not dictate that authors must set all their content to the specified metrics. Rather, it specifies that an author's content has the ability to be set to those metrics without the loss of content or functionality. The author requirement is to not to interfere with a user's ability to override the author settings.

If the technologies being used are capable of overriding text to the Success Criterion's metrics, then this SC is applicable. For instance Cascading Style Sheet/HTML technologies are quite able to allow for the specified spacing metrics. Plugin technologies would need to have a built in ability to modify styles to the specified metrics. Currently, this SC can not be reliably tested in PDF user agents.

Examples of text that are typically not affected by style properties are images of text and some types of captions, which are not expected to adapt. @@ Need explanation of what types of captions based on @johnfoliot's November 13 caption comments. (Concern isn't that captions "are open, but some 'open captions' can be done from a separate file. Two ways of achieving it: burn it in, or the player can force them on." Consult with JF for how to word this.)

For this Success Criterion the canvas implementation of text is considered to be images of text. @@ Suggestion from @steverep to move this sentence to the definition of images of text as it affects additional SCs. Leaving it in until when/if consensus is reached and definition is updated.



  1. Spacing can be overridden to the SC's metrics.
  2. Text fits within the bounds of its containing box without being cut off.
  3. Text fits within the bounds of its containing box without overlapping other boxes.