Elements can have different content types.
An XML element is everything from (including) the element's start tag to (including) the element's end tag.
An element can have element content, mixed content, simple content, or empty content. An element can also have attributes.
In the example above, book has element content, because it contains other elements. Chapter has mixed content because it contains both text and other elements. Para has simple content (or text content) because it contains only text. Prod has empty content, because it carries no information.
In the example above only the prod element has attributes. The attribute named id has the value "33-657". The attribute named media has the value "paper".