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editor: A software program that packages your keystrokes into files to author text on a computer, one must use an editor. Some editors are fancier than others. The simplest is vi, an old but still kicking Unix editor. Emacs is a nice editor with lots of configuration potential, but a somewhat steep learning curve and no style presentation. Both of these editors display the text and markup together, which can make authoring difficult for those who aren't used to seeing all the tags in the content. See also document, markup.

element: A defined piece of an XML document. XML elements are denoted by start and end tags, and can contain data and other elements in a specified hierarchy. See also attribute, content, markup.

empty element: An element that is comprised of a single tag and contains no content data. An empty element begins with an opening angle bracket (<), followed by the element name, any attributes and their values, and closed with a slash and closing angle bracket (/>). See also attribute, content, element.

entity: A name assigned by means of declaration to some chunk of data. Some entities have been predefined for special characters such as <, >, and & that cannot be used directly in the content of an XML document because they would conflict with the markup. See also entity reference, markup.

entity reference: A special string that refers to an entity, indicated by a starting & and an ending semicolon. Entity references occur in text and are parsed by the XML processor. See also entity.

external entity: An entity that refers to another document. See also entity, file, URL.

external subset: A group of declarations, comprising all or part of a document type definition, that is stored in an external entity and referenced from a document's DTD using a public or system identifier. See also document, DTD.