What is XML Used For?
XML documents are used to transfer data from one
place to another often over the Internet.
XML subsets are designed for particular applications.
One is RSS (Rich Site Summary or Really Simple
Syndication ).  It is used to send breaking news bulletins
from one web site to another.
A number of fields have their own subsets.  These
include chemistry, mathematics, and  books publishing.
Most of these subsets are registered with the
W3Consortium and are available for anyone’s use.