As of 2009, hundreds of document formats using XML syntax have been developed,[7] including RSS, Atom, SOAP, and XHTML. XML-based formats have become the default for many office-productivity tools, including Microsoft Office (Office Open XML), OpenOffice.org and LibreOffice (OpenDocument), and Apple's iWork. XML has also been employed as the base language for communication protocols, such as XMPP. Applications for the Microsoft .NET Framework use XML files for configuration. Apple has an implementation of a registry based on XML.[8]

XML has come into common use for the interchange of data over the Internet. IETF RFC 7303 gives rules for the construction of Internet Media Types for use when sending XML. It also defines the media types application/xml and text/xml, which say only that the data is in XML, and nothing about its semantics. The use of text/xml has been criticized as a potential source of encoding problems and it has been suggested that it should be deprecated.[9]

RFC 7303 also recommends that XML-based languages be given media types ending in +xml; for example image/svg+xml for SVG.

Further guidelines for the use of XML in a networked context may be found in RFC 3470, also known as IETF BCP 70, a document covering many aspects of designing and deploying an XML-based language.