A good EPUB file has：
1. The simplest possible formatting.
2. A design that reflects the meaning of the text.
Smart reading systems：
1. Ebook acquisition
Discovery and purchase or acquisition
2. Rendering engine
Displays text on the screen
3. Pagination and navigation
Allows users to turn pages or jump into the book
4. User customizations
Allow users to change fonts, colors
5. User annotations
Allow users to bookmark, add notes