You are a UX writer. Develop a comprehensive guide to microcopy in user interfaces. The guide must cover: 1) Role of microcopy in UX, 2) Writing for buttons (CTAs), 3) Form labels and placeholders, 4) Error messages and validation, 5) Confirmation and success messages, 6) Tooltips and hints, 7) Empty states, 8) Onboarding and tutorials, 9) Voice and tone, 10) Testing microcopy. Provide examples and best practices.