Use Canvas's default text size, color, and font or:
- Use san serif font for digital paragraph text instead of serif font.
- Do not use paragraph text that is smaller than 12pt.
- Avoid using font sizes that cause paragraph text to be the same size or larger than headings.
- Avoid using pure black text on pure white background or the reverse.
Use bold formatting for emphasis, but avoid overusing bold formatting.
Avoid italics outside of MLA, APA, etc. citations. The occasional 1-2 word emphasis might be acceptable though.
Avoid underlines and/or blue font on non-linked text.
Do not justify align paragraph text and generally avoid center, or right aligning paragraph text.
Avoid using ALL CAPS.
Use a single space instead of double space between sentences.

Benefits

These recommendations are considered generally beneficial to everyone, but especially persons with low vision and/or with reading disorders like Dyslexia. The following explains how:

Blurred view of Julius Caesar quotation in different fonts

Avoiding text written in all uppercase, in serif font, with underlines, and/or in italics can make reading less difficult as it reduces interference with the ability to identify letters and words.
Similarly, avoiding paragraph text that is larger than heading text makes it easier to recognize the hierarchy of information on the page.
Using text that is no smaller than 12pt font better ensures readability by all persons, including those with low vision and those on mobile devices.
Avoiding pure black text on a pure white background or the reverse can prevent some people from seeing the letters as blurry or as if they have one or more shadows.
Avoiding justify alignment and putting one space between sentences instead of two or more can prevent "rivers" of space from forming on the page, which have been known to distract to some readers and make it difficult for others to stay on the correct line while reading.
Avoiding center and left alignment can make it easier for persons with low vision or mobile devices to locate content on the page. Many web pages and document designs have trained us to look to the left margin to find content, so centered or right-aligned content may go unnoticed, especially if the screen is zoomed in.
Not using blue and/or underlined text can keep your audience from attempting to click non-link text.

Why Are These Recommended?

There are multiple factors that go into why these features are recommended instead of being required. Perhaps the main reason is that the effectiveness of a lot of these practices is still widely debated.

For example, let's look at the serif vs. san serif point. In this point, it is recommended that fonts which do not have little flairs or feet at the ends of the letters' strokes (san serif font) be used for digital text. However, the amount by which this practice improves readability is still widely debated.

If the above description of serif and san serif fonts was unclear, read WebAIM's Fonts page or WebDesignerDepot's post on UrbanFont's infographic to get a better understanding before reading the rest of this section.

Back in the printing press days, the flairs or serifs were thought to help readers read full lines of text instead of starting on one line and ending up on another at some point in the middle of the reading. It's possible that this was true because of the quality of print back then. Likewise, computer screens may have had an impact on the start of this practice in that older computer screens, especially those of the 1980s and 1990s, may have made it difficult to distinguish letters of serif fonts. For example, a lowercase r next to a lowercase n could look very much like a lowercase m. Granted, the same could be said of certain san serif fonts with narrow letter spacing. Now that computer screens have much clearer graphics, the readability of the two font families may not make much difference.

Still, one font family must be used over the other. Certain advocates of using san serif font for digital texts claim that it helps persons with dyslexia or vision impairments (American Federation for the Blind, Anthony, Robin Collinge). Still, there are persons with such conditions that prefer serif font for digital text. Also, as of yet, there appears to be no study that is able to produce a statistically significant difference in the readability of either font family (WebAIM, Poole). But again, one font family must be chosen over another. Luckily, the decision doesn't have to be that daunting. There is technology like your web browser's settings and add-ons like Stylebot that can allow people to set whichever font family they prefer.

Between the debates and the growing ability to customize your experience, it makes sense that WCAG wouldn't require one font family over the other. However, the makers of WCAG may have one more reason for not requiring this criteria. One of the characteristics that makes WCAG such a useful and internationally accepted standard is that the guidelines does its best to be technology agnostic or applicable to as many digital technologies--current and future--as possible. By requiring the practice recommended here, it could interfere with this quality.

With regard to the remaining recommendations, the font-size practices may have been excluded for all of the same reasons. The bold, italic, underline, and all uppercase practices may have been similarly excluded but there is probably more definitive research supporting these practices, especially regarding italics and all uppercase. With regards to justified alignment, WCAG actually has WCAG 1.4.8 , a level AAA criteria, which says you shouldn't justify text. However, because it is an AAA criteria, it isn't required.

Additional Reading

Last Updated Summer 2018