Adapting Text

From Low Vision Accessibility Task Force
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Open Issues and Survey Results

(Links to surveys require W3C Member access)

SC Shortname

Adapting text

Note: This SC merges 79 Font Family, 78 Spacing, and 74 Text Color as they are very similar in aim (ability to override and adapt text).

SC Text

If the technologies being used allow the user agent to adaptstyle properties of text, then no loss of essential content or functionality occurs by adapting all of the following:

  1. line height (line spacing) to at least 1.5 times the font size
  2. spacing underneath paragraphs to at least 2 times the font size
  3. letter spacing (tracking) to at least 0.12 times the font size
  4. word spacing to at least 0.16 times the font size

Note: Examples of text that are typically not affected by style properties are open captions and images of text, which are not expected to adapt.

Editor's note: The Working Group seeks to include overriding text color, background color, and font-family as part of this SC, but is not yet able to identify a way to do so that is sufficiently testable.

Suggested Priority Level

Level AA

Related Glossary additions or changes

adapted
Formatting being overridden by the client.
Style Properties
Properties whose values determine the presentation (e.g. font, color, size, location, padding, volume, synthesized speech prosody) of content elements as they are rendered (e.g. onscreen, via loudspeaker, via braille display) by user agents. Style properties can have several origins:
  • user agent default styles: The default style property values applied in the absence of any author or user styles. Some web content technologies specify a default rendering; others do not.
  • author styles: Style property values that are set by the author as part of the content (e.g. in-line styles, author style sheets).
  • user styles: Style property values that are set by the user (e.g. via user agent interface settings, user style sheets).

What Principle and Guideline the SC falls within.

Principle 1, Guideline 1.4

Description

The intent of this Success Criterion is to help ensure that people with low vision can override font family, text colors, and spacing. People with low vision often must override author settings via user stylesheet, bookmarklet, extension or application such as VIP-PDF Reader.

This SC sets metrics for a normative testable values. Any particular user is likely to choose different values (especially font & color).

The principle is that if you override the font (with any font), the issues appear. E.g. font-icons disappear. Same for colors, the act of changing them at all will highlight most or all issues people would get from changing them to their preferred colors.

Line-height, letter-spacing, and word-spacing metrics were chosen as measures based on Research. McLeish ran from .04 to .25 em tests (Wayne E. Dick PhD analyzed the McLeish study and translated from points). McLeish found an increasing curve in reading speed of actual materials up to .25, but it really started to flatten at .20. Previous studies that reported no improvement started at .5em. Right at the flat point. Hence Wayne recommends letter spacing be 0.12em, and word spacing be 0.16em for this SC.

The plan is to start testing sites with these metrics on the various user-agent tools, primarily bookmarklets created specifically for this. See where problems surface. Adjust measures if needed. And then provide techniques.

Benefits

Font Family

Some fonts/typefaces are more readable than others. For example, some people cannot read fonts with sub-pixel rendering...

User Need: Users can change the font face (also called font family or typeface) of all text, choosing from a wide range of fonts including sans serif and serif fonts..

Source: Accessibility Requirements for People with Low Vision, Section 3.3.2

Text Color

...some people need low brightness, especially for backgrounds. Some people, who need low brightness for backgrounds, also need low brightness overall, and thus need low-brightness text.

Other people need high contrast between text and background, including many older people who lose contrast sensitivity from ageing. Some read better with dark text on a light background.

For some people, common color combinations or colors from a limited color palette work fine. For example, black text on a white background, or the inverse, with white text on a black background. Other people need to select more-specific background and text colors. For example, people, who require low brightness overall, need to select the specific background and text colors that provide sufficient contrast for them, yet not too-high brightness. Readable and optimal color combinations differ vastly among individuals, and can even vary from one individual to another, depending upon conditions such as fatigue and lighting.

Figure 8: Web page with author-defined colors with low contrast - light background, gray text, light green headings:

screen capture

Figure 9: Web page with user style with medium contrast - brown background, tan text, headings of different dull colors:

screen capture

Figure 10: Web page with user style with high contrast - black background, white text, headings of different bright colors

screen capture

User Need - Contrast: Users can set the background color and the text color from the full color spectrum.

Source: Accessibility Requirements for People with Low Vision, Section 3.1.2 Text Contrast

Spacing

Spacing such as space between lines and space between words impacts readability.

The space between lines in a block of text is also called leading. Some people need more space between lines to be able to read text. Line spacing also helps with tracking.

User Need: Line Spacing: Users can change the line spacing (leading) for blocks of text.

Source: Accessibility Requirements for People with Low Vision, Section 3.4.1

Some people need more space between letters to read text.

User Need: Letter Spacing: Users can change the letter spacing (space between letters/characters) of blocks of text.

Source: Accessibility Requirements for People with Low Vision, Section 3.4.2

Some people need more space between words to read text.

User Need: Word Spacing: Users can change the word spacing (space between words) of blocks of text.

Source: Accessibility Requirements for People with Low Vision, Section 3.4.3

Testability

Using a bookmarklet, user stylesheet, or VIP-PDF Reader change:

  1. line height (line spacing) to at least 1.5 times the font size
  2. spacing underneath paragraphs to at least 2 times the font size
  3. letter spacing (tracking) to at least 0.12 times the font size
  4. word spacing to at least 0.16 times the font size
  5. font family to a different font family (e.g. Verdana if that is not in use)
  6. foreground color and background color to a different foreground color and background color (e.g. white on black if that combination is not in use)

Expected Results

  • No loss of content or functionality.

Techniques

Existing Related Techniques

New Techniques

Related Information

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Public and Member Comments

Research

Tools

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