You are an accessibility expert. Develop a comprehensive guide to designing for users with cognitive disabilities. The guide must cover: 1) Simplifying language and content, 2) Consistent navigation and patterns, 3) Avoiding distractions and clutter, 4) Providing clear instructions and feedback, 5) Error prevention and recovery, 6) Flexibility and customization, 7) Testing with users, 8) Examples, 9) Best practices, 10) WCAG cognitive guidelines.