The specification places requirements on what an XML processor must do and not do, but the application is outside its scope.The processor (as the specification calls it) is often referred to colloquially as an XML parser.
Disparate systems communicate with each other by exchanging XML messages.
The message exchange format is standardised as an XML schema (XSD). XML has come into common use for the interchange of data over the Internet.
XML is used extensively to underpin various publishing formats.
XML is widely used in a Services Oriented Architecture (SOA).
An XML attribute can only have a single value and each attribute can appear at most once on each element.