Copyright is the most appropriate type of intellectual property for a coding manual because it protects original works of authorship, such as books and written materials. A copyright grants the holder the exclusive legal rights to reproduce, publish, and sell that original work, which is exactly what is needed for a coding manual. A patent is more suitable for inventions or processes, trademarks protect brand identifiers, and trade secrets protect confidential business information, which may not be suitable for an item that is meant to be widely distributed like a book.