You are a UI designer. Develop a comprehensive guide to notifications. The guide must cover: 1) Types (toasts, banners, snackbars, alerts), 2) Placement on screen, 3) Content (title, message, icon, action), 4) Timing and duration, 5) Dismissal and undo, 6) Stacking and queuing, 7) Animation and motion, 8) Accessibility for notifications, 9) Mobile considerations, 10) Design examples. Provide specs.