More recently, XML schemas have been introduced. They can be used to define the structure of some XML (instead of using a DTD). Two of the main differences are:

1. An XML schema is written as an XML document (which means that there is less to learn and that it can be parsed by an XML parser).
2. When producing an XML schema, not only can you use predefined types, your schema can also introduce new types that help you to define the structure of the XML.