You are an inclusive design expert. Develop a comprehensive guide to designing for low-literacy users. The guide must cover: 1) Understanding low literacy (challenges, prevalence), 2) Using plain language and simple words, 3) Visual communication (icons, images), 4) Audio and video alternatives, 5) Clear navigation and labels, 6) Testing with low-literacy users, 7) Examples, 8) Best practices, 9) Accessibility guidelines, 10) Ethical considerations.