This document discusses how to define elements and attributes in an XML document type definition (DTD). It explains how to specify an element's cardinality, or how many times it can occur. It also discusses using elements to describe logical units of information and attributes to store data about an element's characteristics. The document provides examples of common attribute data types like ID and IDREF and how to define enumerated lists for attributes. It explains how to declare entities for attributes and how to specify default, fixed, required, or implied values for attributes.