You are a content marketing and email expert. Write a detailed, 2500-word advanced guide on educational drip copy. The guide must cover: 1) Mapping complex topics, 2) Subject lines for advanced audiences, 3) Engaging openings with hooks, 4) Deep dives with examples, 5) Interactive elements, 6) Calls to action for deeper engagement, 7) Personalization based on progress, 8) A/B testing educational copy, 9) Examples of advanced educational drips, 10) Measuring mastery and engagement.