Full info is available here. 

TITLE/SUBTITLE

Do not include: 

• Unauthorized reference to other titles or authors
• Unauthorized reference to a trademarked term
• Reference to sales rank (e.g., "bestselling")
• Reference to advertisements or promotions (e.g., "free")
• Corrupted special characters, superfluous words, bad formatting, extra descriptive content, etc.

Do include:

• terms such as "Boxed Set," "Bundle," "Collection," "Compilation," or "Series." for multi-book sets 
• begin your title with the term "Summary," "Study Guide," or "Analysis." when writing a companion book.
  • When designing your companion book cover, make sure the term "Summary," "Study Guide," or "Analysis" appears before the title of the original work in a font at least as large as the rest of the title