Support flexibility and adaptation ✎

Content does not restrict its view and operation to a single display orientation, such as portrait or landscape, unless a specific display orientation is essential (i.e., bank check). 

Use responsive design to allow your content to zoom and respond to various screen sizes.

People with a variety of print disabilities (including low vision, dyslexia, other cognitive disabilities) can benefit from being able to increase the spacing between lines, words, and/or letters on their own device.

Paragraphs of text are a fundamental core of web content. It's important to display them in a fashion that is optimally readable to the majority of your audience.

When text is presented as an image of text, that limits peoples' ability to change the appearance of that text. So wherever possible, use text along with CSS to apply styling.

There are a number of ways to zoom web-page content in to enlarge text without needing to provide explicit controls to do so. To avoid diminishing this variety of user control, you have to be careful how you code font sizes.