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In the Standard Generalized Markup Language (SGML), an entity is a primitive data type, which associates a string with either a unique alias (such as a user-specified name) or an SGML reserved word (such as #DEFAULT). Entities are foundational to the organizational structure and definition of SGML documents. The SGML specification defines numerous entity types, which are distinguished by keyword qualifiers and context. An entity string value may variously consist of plain text, SGML tags, and/or references to previously-defined entities. Certain entity types may also invoke external documents. Entities are called by reference.==Types of entities== Entities are classified as general or parameter: * A ''general'' entity can only be referenced within the document content. * A ''parameter'' entity can only be referenced within the DTD. Entities are also further classified as parsed or unparsed: * A ''parsed'' entity contains text, which will be incorporated into the document and parsed if the entity is referenced. A parameter entity can only be a parsed entity. * An ''unparsed'' entity contains any kind of data, and a reference to it will result in the application's merely being notified of the entity's presence; the content of the entity will not be parsed, even if it is text. An unparsed entity can only be external. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SGML entity」の詳細全文を読む スポンサード リンク
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