It can be used as a data or document file format, for example HTML is one or an Office file format (all OpenOffice.org files are Xml). The advantage is, that there are lots of tools and APIs available to deal with xml and it can be easily edited by hand.
Microsoft has claimed, that Xml would be a central file format
in .NET.
Entsprechend big is the class library offered to work with Xml.
You can: