The first principle from the Web Content Accessibility Guidelines, Perceivable, focuses on making content available and recognizable for all users, despite the user’s way of perceiving information or the tools they use to access this information; for example, screen readers. In short, content can’t be invisible to all of the user's senses. Here's an excerpt from WCAG 2.0:
"All web content and UI elements must be presentable in a way that the users can perceive, and cannot be hidden from all of the user’s senses."
- Provide text alternatives for non-text content: If visual elements are key for the user to interact with the web page, it should be accompanied by alternative text (sometimes called ALT TEXT) for the screen reader to ...
