nXML mode is an addon for GNU Emacs, which makes GNU Emacs into a powerful XML editor. It's called nXML mode because in Emacs terminology addons that customize Emacs for editing text of a particular sort are called modes. Emacs already has a simple mode for XML; nXML mode is a new mode for XML. You should realize that Emacs with nXML mode differs from most XML editors in that XML is edited as text