line length for blocks of text

[shawna-slh]

Explore options for optimizing line lengths for different configurations, user needs, and preferences. For example, short line length is easier for some people to read; some people with large text want wider text areas; etc...

related issues have more input/background:

• https://github.com/w3c/wai-aria-practices/issues/108
• https://github.com/w3c/wai-minimal-header-design/issues/60
• https://github.com/w3c/wai-website/issues/37