There are also additional abilities to define content models. The advantages of XML include the availability of a large number of evolving tools. Unfortunately, many of the associated standards are still evolving, and the tools will have to follow along. This means that developing a robust tool set that uses more than the basic XML 1.0 recommendation is not possible in the short term. The promised availability of a wide variety of high-quality tools which support some of the most important related standards is not immediate.
Many tools are likely to be free.