XML (extensible markup language)
- A metalanguage containing a set of rules for constructing other markup languages.
With XML, people can make up their own tags, which expands the amount and kinds
of information that can be provided about the data held in documents. It
enables designers to create their own customized tags to provide functionality
not available with HTML. For example, XML supports links that point to multiple
documents, as opposed to HTML links, which can reference just one destination
each.