Using XML, authors can create new tags at will, even very complex ones. They also can use XML DTDs to validate the structure of large numbers of documents, which is important when importing the data from those documents into other applications. XML is also fully SGML-compatible. Because XML documents are readable by SGML software, organizations with an investment in SGML can use XML right away. However, since XML is a subset of SGML, it can't read all SGML documents.
Organizations can use XML to ease the exchange of information between disparate applications.
For example, the Chemical Markup Language is an XML-compatible markup language with specific extensions for describing molecules and compounds. Using the DTD for that language, a developer could create a filter to import data points from a Web page into a proprietary chemical modeling application. Developers also will be able to create clients that are more intelligent. In addition, XML will make intelligent agents easier to design and deploy. Today, agent software has to jump through hoops to recognize the right data points on constantly changing Web pages.